957 lines
46 KiB
HTML
957 lines
46 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<!--[if IE]><meta http-equiv="X-UA-Compatible" content="IE=edge"><![endif]-->
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta name="generator" content="Asciidoctor 1.5.8">
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<title>Git pack format</title>
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<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700">
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<style>
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/* Asciidoctor default stylesheet | MIT License | http://asciidoctor.org */
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/* Uncomment @import statement below to use as custom stylesheet */
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/*@import "https://fonts.googleapis.com/css?family=Open+Sans:300,300italic,400,400italic,600,600italic%7CNoto+Serif:400,400italic,700,700italic%7CDroid+Sans+Mono:400,700";*/
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article,aside,details,figcaption,figure,footer,header,hgroup,main,nav,section,summary{display:block}
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audio,canvas,video{display:inline-block}
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audio:not([controls]){display:none;height:0}
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script{display:none!important}
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html{font-family:sans-serif;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%}
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a{background:transparent}
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a:focus{outline:thin dotted}
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a:active,a:hover{outline:0}
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h1{font-size:2em;margin:.67em 0}
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abbr[title]{border-bottom:1px dotted}
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b,strong{font-weight:bold}
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dfn{font-style:italic}
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hr{-moz-box-sizing:content-box;box-sizing:content-box;height:0}
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mark{background:#ff0;color:#000}
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code,kbd,pre,samp{font-family:monospace;font-size:1em}
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pre{white-space:pre-wrap}
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q{quotes:"\201C" "\201D" "\2018" "\2019"}
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small{font-size:80%}
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sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline}
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sup{top:-.5em}
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sub{bottom:-.25em}
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img{border:0}
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svg:not(:root){overflow:hidden}
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figure{margin:0}
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fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em}
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legend{border:0;padding:0}
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button,input,select,textarea{font-family:inherit;font-size:100%;margin:0}
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button,input{line-height:normal}
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button,select{text-transform:none}
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button,html input[type="button"],input[type="reset"],input[type="submit"]{-webkit-appearance:button;cursor:pointer}
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button[disabled],html input[disabled]{cursor:default}
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input[type="checkbox"],input[type="radio"]{box-sizing:border-box;padding:0}
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button::-moz-focus-inner,input::-moz-focus-inner{border:0;padding:0}
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textarea{overflow:auto;vertical-align:top}
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table{border-collapse:collapse;border-spacing:0}
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*,*::before,*::after{-moz-box-sizing:border-box;-webkit-box-sizing:border-box;box-sizing:border-box}
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html,body{font-size:100%}
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body{background:#fff;color:rgba(0,0,0,.8);padding:0;margin:0;font-family:"Noto Serif","DejaVu Serif",serif;font-weight:400;font-style:normal;line-height:1;position:relative;cursor:auto;tab-size:4;-moz-osx-font-smoothing:grayscale;-webkit-font-smoothing:antialiased}
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a:hover{cursor:pointer}
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img,object,embed{max-width:100%;height:auto}
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object,embed{height:100%}
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img{-ms-interpolation-mode:bicubic}
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.left{float:left!important}
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.right{float:right!important}
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.text-left{text-align:left!important}
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.text-right{text-align:right!important}
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.text-center{text-align:center!important}
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.text-justify{text-align:justify!important}
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.hide{display:none}
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img,object,svg{display:inline-block;vertical-align:middle}
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textarea{height:auto;min-height:50px}
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select{width:100%}
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.stretch{width:100%}
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.subheader,.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{line-height:1.45;color:#7a2518;font-weight:400;margin-top:0;margin-bottom:.25em}
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a{color:#2156a5;text-decoration:underline;line-height:inherit}
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a:hover,a:focus{color:#1d4b8f}
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a img{border:none}
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p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
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h1 small,h2 small,h3 small,#toctitle small,.sidebarblock>.content>.title small,h4 small,h5 small,h6 small{font-size:60%;color:#e99b8f;line-height:0}
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h1{font-size:2.125em}
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h2{font-size:1.6875em}
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h4,h5{font-size:1.125em}
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h6{font-size:1em}
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hr{border:solid #dddddf;border-width:1px 0 0;clear:both;margin:1.25em 0 1.1875em;height:0}
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strong,b{font-weight:bold;line-height:inherit}
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small{font-size:60%;line-height:inherit}
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code{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;color:rgba(0,0,0,.9)}
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ul,ol,dl{font-size:1em;line-height:1.6;margin-bottom:1.25em;list-style-position:outside;font-family:inherit}
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ul,ol{margin-left:1.5em}
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ul.square li ul,ul.circle li ul,ul.disc li ul{list-style:inherit}
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ul.square{list-style-type:square}
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ul.circle{list-style-type:circle}
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ul.disc{list-style-type:disc}
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ol li ul,ol li ol{margin-left:1.25em;margin-bottom:0}
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dl dt{margin-bottom:.3125em;font-weight:bold}
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dl dd{margin-bottom:1.25em}
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abbr,acronym{text-transform:uppercase;font-size:90%;color:rgba(0,0,0,.8);border-bottom:1px dotted #ddd;cursor:help}
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abbr{text-transform:none}
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blockquote{margin:0 0 1.25em;padding:.5625em 1.25em 0 1.1875em;border-left:1px solid #ddd}
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blockquote cite::before{content:"\2014 \0020"}
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blockquote,blockquote p{line-height:1.6;color:rgba(0,0,0,.85)}
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h1{font-size:2.75em}
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h2{font-size:2.3125em}
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h3,#toctitle,.sidebarblock>.content>.title{font-size:1.6875em}
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h4{font-size:1.4375em}}
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table{background:#fff;margin-bottom:1.25em;border:solid 1px #dedede}
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table thead,table tfoot{background:#f7f8f7}
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table thead tr th,table thead tr td,table tfoot tr th,table tfoot tr td{padding:.5em .625em .625em;font-size:inherit;color:rgba(0,0,0,.8);text-align:left}
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table tr th,table tr td{padding:.5625em .625em;font-size:inherit;color:rgba(0,0,0,.8)}
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table tr.even,table tr.alt,table tr:nth-of-type(even){background:#f8f8f7}
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table thead tr th,table tfoot tr th,table tbody tr td,table tr td,table tfoot tr td{display:table-cell;line-height:1.6}
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h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{line-height:1.2;word-spacing:-.05em}
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h1 strong,h2 strong,h3 strong,#toctitle strong,.sidebarblock>.content>.title strong,h4 strong,h5 strong,h6 strong{font-weight:400}
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.clearfix::before,.clearfix::after,.float-group::before,.float-group::after{content:" ";display:table}
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.clearfix::after,.float-group::after{clear:both}
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*:not(pre)>code{font-size:.9375em;font-style:normal!important;letter-spacing:0;padding:.1em .5ex;word-spacing:-.15em;background-color:#f7f7f8;-webkit-border-radius:4px;border-radius:4px;line-height:1.45;text-rendering:optimizeSpeed;word-wrap:break-word}
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*:not(pre)>code.nobreak{word-wrap:normal}
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*:not(pre)>code.nowrap{white-space:nowrap}
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pre,pre>code{line-height:1.45;color:rgba(0,0,0,.9);font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;font-weight:400;text-rendering:optimizeSpeed}
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em em{font-style:normal}
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strong strong{font-weight:400}
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.keyseq{color:rgba(51,51,51,.8)}
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kbd{font-family:"Droid Sans Mono","DejaVu Sans Mono",monospace;display:inline-block;color:rgba(0,0,0,.8);font-size:.65em;line-height:1.45;background-color:#f7f7f7;border:1px solid #ccc;-webkit-border-radius:3px;border-radius:3px;-webkit-box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em white inset;box-shadow:0 1px 0 rgba(0,0,0,.2),0 0 0 .1em #fff inset;margin:0 .15em;padding:.2em .5em;vertical-align:middle;position:relative;top:-.1em;white-space:nowrap}
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.keyseq kbd:first-child{margin-left:0}
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.keyseq kbd:last-child{margin-right:0}
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.menuseq,.menuref{color:#000}
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.menuseq b:not(.caret),.menuref{font-weight:inherit}
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.menuseq{word-spacing:-.02em}
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.menuseq b.caret{font-size:1.25em;line-height:.8}
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.menuseq i.caret{font-weight:bold;text-align:center;width:.45em}
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b.button::before,b.button::after{position:relative;top:-1px;font-weight:400}
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b.button::before{content:"[";padding:0 3px 0 2px}
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b.button::after{content:"]";padding:0 2px 0 3px}
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p a>code:hover{color:rgba(0,0,0,.9)}
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#header,#content,#footnotes,#footer{width:100%;margin-left:auto;margin-right:auto;margin-top:0;margin-bottom:0;max-width:62.5em;*zoom:1;position:relative;padding-left:.9375em;padding-right:.9375em}
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#header::before,#header::after,#content::before,#content::after,#footnotes::before,#footnotes::after,#footer::before,#footer::after{content:" ";display:table}
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#header::after,#content::after,#footnotes::after,#footer::after{clear:both}
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#content{margin-top:1.25em}
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#content::before{content:none}
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#header>h1:first-child{color:rgba(0,0,0,.85);margin-top:2.25rem;margin-bottom:0}
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#header>h1:first-child+#toc{margin-top:8px;border-top:1px solid #dddddf}
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#header .details{border-bottom:1px solid #dddddf;line-height:1.45;padding-top:.25em;padding-bottom:.25em;padding-left:.25em;color:rgba(0,0,0,.6);display:-ms-flexbox;display:-webkit-flex;display:flex;-ms-flex-flow:row wrap;-webkit-flex-flow:row wrap;flex-flow:row wrap}
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#header .details span:first-child{margin-left:-.125em}
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#header .details span.email a{color:rgba(0,0,0,.85)}
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#header .details br{display:none}
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#header .details br+span::before{content:"\00a0\2013\00a0"}
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#header .details br+span.author::before{content:"\00a0\22c5\00a0";color:rgba(0,0,0,.85)}
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#header .details br+span#revremark::before{content:"\00a0|\00a0"}
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#header #revnumber{text-transform:capitalize}
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#header #revnumber::after{content:"\00a0"}
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#content>h1:first-child:not([class]){color:rgba(0,0,0,.85);border-bottom:1px solid #dddddf;padding-bottom:8px;margin-top:0;padding-top:1rem;margin-bottom:1.25rem}
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#toc{border-bottom:1px solid #e7e7e9;padding-bottom:.5em}
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#toc>ul{margin-left:.125em}
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#toc ul.sectlevel0>li>a{font-style:italic}
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#toc ul.sectlevel0 ul.sectlevel1{margin:.5em 0}
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#toc ul{font-family:"Open Sans","DejaVu Sans",sans-serif;list-style-type:none}
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#toc li{line-height:1.3334;margin-top:.3334em}
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#toc a{text-decoration:none}
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#toc a:active{text-decoration:underline}
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#toctitle{color:#7a2518;font-size:1.2em}
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@media screen and (min-width:768px){#toctitle{font-size:1.375em}
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body.toc2{padding-left:15em;padding-right:0}
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#toc.toc2{margin-top:0!important;background-color:#f8f8f7;position:fixed;width:15em;left:0;top:0;border-right:1px solid #e7e7e9;border-top-width:0!important;border-bottom-width:0!important;z-index:1000;padding:1.25em 1em;height:100%;overflow:auto}
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body.toc2.toc-right{padding-left:0;padding-right:15em}
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body.toc2.toc-right #toc.toc2{border-right-width:0;border-left:1px solid #e7e7e9;left:auto;right:0}}
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@media screen and (min-width:1280px){body.toc2{padding-left:20em;padding-right:0}
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#toc.toc2{width:20em}
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#toc.toc2 ul ul{padding-left:1.25em}
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body.toc2.toc-right{padding-left:0;padding-right:20em}}
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#content #toc{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
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#content #toc>:first-child{margin-top:0}
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#content #toc>:last-child{margin-bottom:0}
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#footer{max-width:100%;background-color:rgba(0,0,0,.8);padding:1.25em}
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#footer-text{color:rgba(255,255,255,.8);line-height:1.44}
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#content{margin-bottom:.625em}
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.sect1{padding-bottom:.625em}
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@media screen and (min-width:768px){#content{margin-bottom:1.25em}
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.sect1{padding-bottom:1.25em}}
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.sect1:last-child{padding-bottom:0}
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.sect1+.sect1{border-top:1px solid #e7e7e9}
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#content h1>a.anchor,h2>a.anchor,h3>a.anchor,#toctitle>a.anchor,.sidebarblock>.content>.title>a.anchor,h4>a.anchor,h5>a.anchor,h6>a.anchor{position:absolute;z-index:1001;width:1.5ex;margin-left:-1.5ex;display:block;text-decoration:none!important;visibility:hidden;text-align:center;font-weight:400}
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#content h1>a.anchor::before,h2>a.anchor::before,h3>a.anchor::before,#toctitle>a.anchor::before,.sidebarblock>.content>.title>a.anchor::before,h4>a.anchor::before,h5>a.anchor::before,h6>a.anchor::before{content:"\00A7";font-size:.85em;display:block;padding-top:.1em}
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#content h1:hover>a.anchor,#content h1>a.anchor:hover,h2:hover>a.anchor,h2>a.anchor:hover,h3:hover>a.anchor,#toctitle:hover>a.anchor,.sidebarblock>.content>.title:hover>a.anchor,h3>a.anchor:hover,#toctitle>a.anchor:hover,.sidebarblock>.content>.title>a.anchor:hover,h4:hover>a.anchor,h4>a.anchor:hover,h5:hover>a.anchor,h5>a.anchor:hover,h6:hover>a.anchor,h6>a.anchor:hover{visibility:visible}
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#content h1>a.link,h2>a.link,h3>a.link,#toctitle>a.link,.sidebarblock>.content>.title>a.link,h4>a.link,h5>a.link,h6>a.link{color:#ba3925;text-decoration:none}
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#content h1>a.link:hover,h2>a.link:hover,h3>a.link:hover,#toctitle>a.link:hover,.sidebarblock>.content>.title>a.link:hover,h4>a.link:hover,h5>a.link:hover,h6>a.link:hover{color:#a53221}
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.audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
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.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{text-rendering:optimizeLegibility;text-align:left;font-family:"Noto Serif","DejaVu Serif",serif;font-size:1rem;font-style:italic}
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table.tableblock.fit-content>caption.title{white-space:nowrap;width:0}
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.paragraph.lead>p,#preamble>.sectionbody>[class="paragraph"]:first-of-type p{font-size:1.21875em;line-height:1.6;color:rgba(0,0,0,.85)}
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table.tableblock #preamble>.sectionbody>[class="paragraph"]:first-of-type p{font-size:inherit}
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.admonitionblock>table{border-collapse:separate;border:0;background:none;width:100%}
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.admonitionblock>table td.icon{text-align:center;width:80px}
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.admonitionblock>table td.icon img{max-width:none}
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.admonitionblock>table td.icon .title{font-weight:bold;font-family:"Open Sans","DejaVu Sans",sans-serif;text-transform:uppercase}
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.admonitionblock>table td.content{padding-left:1.125em;padding-right:1.25em;border-left:1px solid #dddddf;color:rgba(0,0,0,.6)}
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.admonitionblock>table td.content>:last-child>:last-child{margin-bottom:0}
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.exampleblock>.content{border-style:solid;border-width:1px;border-color:#e6e6e6;margin-bottom:1.25em;padding:1.25em;background:#fff;-webkit-border-radius:4px;border-radius:4px}
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.exampleblock>.content>:first-child{margin-top:0}
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.exampleblock>.content>:last-child{margin-bottom:0}
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.sidebarblock{border-style:solid;border-width:1px;border-color:#e0e0dc;margin-bottom:1.25em;padding:1.25em;background:#f8f8f7;-webkit-border-radius:4px;border-radius:4px}
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.sidebarblock>:first-child{margin-top:0}
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.sidebarblock>:last-child{margin-bottom:0}
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.sidebarblock>.content>.title{color:#7a2518;margin-top:0;text-align:center}
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.exampleblock>.content>:last-child>:last-child,.exampleblock>.content .olist>ol>li:last-child>:last-child,.exampleblock>.content .ulist>ul>li:last-child>:last-child,.exampleblock>.content .qlist>ol>li:last-child>:last-child,.sidebarblock>.content>:last-child>:last-child,.sidebarblock>.content .olist>ol>li:last-child>:last-child,.sidebarblock>.content .ulist>ul>li:last-child>:last-child,.sidebarblock>.content .qlist>ol>li:last-child>:last-child{margin-bottom:0}
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.literalblock pre,.listingblock pre:not(.highlight),.listingblock pre[class="highlight"],.listingblock pre[class^="highlight "],.listingblock pre.CodeRay,.listingblock pre.prettyprint{background:#f7f7f8}
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.sidebarblock .literalblock pre,.sidebarblock .listingblock pre:not(.highlight),.sidebarblock .listingblock pre[class="highlight"],.sidebarblock .listingblock pre[class^="highlight "],.sidebarblock .listingblock pre.CodeRay,.sidebarblock .listingblock pre.prettyprint{background:#f2f1f1}
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.literalblock pre,.literalblock pre[class],.listingblock pre,.listingblock pre[class]{-webkit-border-radius:4px;border-radius:4px;word-wrap:break-word;overflow-x:auto;padding:1em;font-size:.8125em}
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pre .conum[data-value]{position:relative;top:-.125em}
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b.conum *{color:inherit!important}
|
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|
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|
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p{margin-bottom:1.25rem}
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.print-only{display:none!important}
|
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@page{margin:1.25cm .75cm}
|
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@media print{*{-webkit-box-shadow:none!important;box-shadow:none!important;text-shadow:none!important}
|
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html{font-size:80%}
|
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a{color:inherit!important;text-decoration:underline!important}
|
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a.bare,a[href^="#"],a[href^="mailto:"]{text-decoration:none!important}
|
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a[href^="http:"]:not(.bare)::after,a[href^="https:"]:not(.bare)::after{content:"(" attr(href) ")";display:inline-block;font-size:.875em;padding-left:.25em}
|
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abbr[title]::after{content:" (" attr(title) ")"}
|
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pre,blockquote,tr,img,object,svg{page-break-inside:avoid}
|
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thead{display:table-header-group}
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svg{max-width:100%}
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p,blockquote,dt,td.content{font-size:1em;orphans:3;widows:3}
|
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h2,h3,#toctitle,.sidebarblock>.content>.title{page-break-after:avoid}
|
|
#toc,.sidebarblock,.exampleblock>.content{background:none!important}
|
|
#toc{border-bottom:1px solid #dddddf!important;padding-bottom:0!important}
|
|
body.book #header{text-align:center}
|
|
body.book #header>h1:first-child{border:0!important;margin:2.5em 0 1em}
|
|
body.book #header .details{border:0!important;display:block;padding:0!important}
|
|
body.book #header .details span:first-child{margin-left:0!important}
|
|
body.book #header .details br{display:block}
|
|
body.book #header .details br+span::before{content:none!important}
|
|
body.book #toc{border:0!important;text-align:left!important;padding:0!important;margin:0!important}
|
|
body.book #toc,body.book #preamble,body.book h1.sect0,body.book .sect1>h2{page-break-before:always}
|
|
.listingblock code[data-lang]::before{display:block}
|
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#footer{padding:0 .9375em}
|
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.hide-on-print{display:none!important}
|
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.print-only{display:block!important}
|
|
.hide-for-print{display:none!important}
|
|
.show-for-print{display:inherit!important}}
|
|
@media print,amzn-kf8{#header>h1:first-child{margin-top:1.25rem}
|
|
.sect1{padding:0!important}
|
|
.sect1+.sect1{border:0}
|
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#footer{background:none}
|
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#footer-text{color:rgba(0,0,0,.6);font-size:.9em}}
|
|
@media amzn-kf8{#header,#content,#footnotes,#footer{padding:0}}
|
|
</style>
|
|
</head>
|
|
<body class="article">
|
|
<div id="header">
|
|
<h1>Git pack format</h1>
|
|
</div>
|
|
<div id="content">
|
|
<div class="sect1">
|
|
<h2 id="_pack_pack_files_have_the_following_format">pack-*.pack files have the following format:</h2>
|
|
<div class="sectionbody">
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>A header appears at the beginning and consists of the following:</p>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>4-byte signature:
|
|
The signature is: {'P', 'A', 'C', 'K'}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre> 4-byte version number (network byte order):
|
|
Git currently accepts version number 2 or 3 but
|
|
generates version 2 only.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>4-byte number of objects contained in the pack (network byte order)</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>Observation: we cannot have more than 4G versions ;-) and
|
|
more than 4G objects in a pack.</pre>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
<li>
|
|
<p>The header is followed by number of object entries, each of
|
|
which looks like this:</p>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>(undeltified representation)
|
|
n-byte type and length (3-bit type, (n-1)*7+4-bit length)
|
|
compressed data</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre> (deltified representation)
|
|
n-byte type and length (3-bit type, (n-1)*7+4-bit length)
|
|
20-byte base object name if OBJ_REF_DELTA or a negative relative
|
|
offset from the delta object's position in the pack if this
|
|
is an OBJ_OFS_DELTA object
|
|
compressed delta data</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>Observation: length of each object is encoded in a variable
|
|
length format and is not constrained to 32-bit or anything.</pre>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
<li>
|
|
<p>The trailer records 20-byte SHA-1 checksum of all of the above.</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_object_types">Object types</h3>
|
|
<div class="paragraph">
|
|
<p>Valid object types are:</p>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>OBJ_COMMIT (1)</p>
|
|
</li>
|
|
<li>
|
|
<p>OBJ_TREE (2)</p>
|
|
</li>
|
|
<li>
|
|
<p>OBJ_BLOB (3)</p>
|
|
</li>
|
|
<li>
|
|
<p>OBJ_TAG (4)</p>
|
|
</li>
|
|
<li>
|
|
<p>OBJ_OFS_DELTA (6)</p>
|
|
</li>
|
|
<li>
|
|
<p>OBJ_REF_DELTA (7)</p>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Type 5 is reserved for future expansion. Type 0 is invalid.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect2">
|
|
<h3 id="_deltified_representation">Deltified representation</h3>
|
|
<div class="paragraph">
|
|
<p>Conceptually there are only four object types: commit, tree, tag and
|
|
blob. However to save space, an object could be stored as a "delta" of
|
|
another "base" object. These representations are assigned new types
|
|
ofs-delta and ref-delta, which is only valid in a pack file.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Both ofs-delta and ref-delta store the "delta" to be applied to
|
|
another object (called <em>base object</em>) to reconstruct the object. The
|
|
difference between them is, ref-delta directly encodes 20-byte base
|
|
object name. If the base object is in the same pack, ofs-delta encodes
|
|
the offset of the base object in the pack instead.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The base object could also be deltified if it’s in the same pack.
|
|
Ref-delta can also refer to an object outside the pack (i.e. the
|
|
so-called "thin pack"). When stored on disk however, the pack should
|
|
be self contained to avoid cyclic dependency.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>The delta data is a sequence of instructions to reconstruct an object
|
|
from the base object. If the base object is deltified, it must be
|
|
converted to canonical form first. Each instruction appends more and
|
|
more data to the target object until it’s complete. There are two
|
|
supported instructions so far: one for copy a byte range from the
|
|
source object and one for inserting new data embedded in the
|
|
instruction itself.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Each instruction has variable length. Instruction type is determined
|
|
by the seventh bit of the first octet. The following diagrams follow
|
|
the convention in RFC 1951 (Deflate compressed data format).</p>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_instruction_to_copy_from_base_object">Instruction to copy from base object</h4>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>+----------+---------+---------+---------+---------+-------+-------+-------+
|
|
| 1xxxxxxx | offset1 | offset2 | offset3 | offset4 | size1 | size2 | size3 |
|
|
+----------+---------+---------+---------+---------+-------+-------+-------+</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This is the instruction format to copy a byte range from the source
|
|
object. It encodes the offset to copy from and the number of bytes to
|
|
copy. Offset and size are in little-endian order.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>All offset and size bytes are optional. This is to reduce the
|
|
instruction size when encoding small offsets or sizes. The first seven
|
|
bits in the first octet determines which of the next seven octets is
|
|
present. If bit zero is set, offset1 is present. If bit one is set
|
|
offset2 is present and so on.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Note that a more compact instruction does not change offset and size
|
|
encoding. For example, if only offset2 is omitted like below, offset3
|
|
still contains bits 16-23. It does not become offset2 and contains
|
|
bits 8-15 even if it’s right next to offset1.</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>+----------+---------+---------+
|
|
| 10000101 | offset1 | offset3 |
|
|
+----------+---------+---------+</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>In its most compact form, this instruction only takes up one byte
|
|
(0x80) with both offset and size omitted, which will have default
|
|
values zero. There is another exception: size zero is automatically
|
|
converted to 0x10000.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_instruction_to_add_new_data">Instruction to add new data</h4>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>+----------+============+
|
|
| 0xxxxxxx | data |
|
|
+----------+============+</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This is the instruction to construct target object without the base
|
|
object. The following data is appended to the target object. The first
|
|
seven bits of the first octet determines the size of data in
|
|
bytes. The size must be non-zero.</p>
|
|
</div>
|
|
</div>
|
|
<div class="sect3">
|
|
<h4 id="_reserved_instruction">Reserved instruction</h4>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>+----------+============
|
|
| 00000000 |
|
|
+----------+============</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>This is the instruction reserved for future expansion.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_original_version_1_pack_idx_files_have_the_following_format">Original (version 1) pack-*.idx files have the following format:</h2>
|
|
<div class="sectionbody">
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>The header consists of 256 4-byte network byte order
|
|
integers. N-th entry of this table records the number of
|
|
objects in the corresponding pack, the first byte of whose
|
|
object name is less than or equal to N. This is called the
|
|
<em>first-level fan-out</em> table.</p>
|
|
</li>
|
|
<li>
|
|
<p>The header is followed by sorted 24-byte entries, one entry
|
|
per object in the pack. Each entry is:</p>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>4-byte network byte order integer, recording where the
|
|
object is stored in the packfile as the offset from the
|
|
beginning.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>20-byte object name.</pre>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
<li>
|
|
<p>The file is concluded with a trailer:</p>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>A copy of the 20-byte SHA-1 checksum at the end of
|
|
corresponding packfile.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>20-byte SHA-1-checksum of all of the above.</pre>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>Pack Idx file:</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre> -- +--------------------------------+
|
|
fanout | fanout[0] = 2 (for example) |-.
|
|
table +--------------------------------+ |
|
|
| fanout[1] | |
|
|
+--------------------------------+ |
|
|
| fanout[2] | |
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
| fanout[255] = total objects |---.
|
|
-- +--------------------------------+ | |
|
|
main | offset | | |
|
|
index | object name 00XXXXXXXXXXXXXXXX | | |
|
|
table +--------------------------------+ | |
|
|
| offset | | |
|
|
| object name 00XXXXXXXXXXXXXXXX | | |
|
|
+--------------------------------+<+ |
|
|
.-| offset | |
|
|
| | object name 01XXXXXXXXXXXXXXXX | |
|
|
| +--------------------------------+ |
|
|
| | offset | |
|
|
| | object name 01XXXXXXXXXXXXXXXX | |
|
|
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
|
|
| | offset | |
|
|
| | object name FFXXXXXXXXXXXXXXXX | |
|
|
--| +--------------------------------+<--+
|
|
trailer | | packfile checksum |
|
|
| +--------------------------------+
|
|
| | idxfile checksum |
|
|
| +--------------------------------+
|
|
.-------.
|
|
|
|
|
Pack file entry: <+</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre> packed object header:
|
|
1-byte size extension bit (MSB)
|
|
type (next 3 bit)
|
|
size0 (lower 4-bit)
|
|
n-byte sizeN (as long as MSB is set, each 7-bit)
|
|
size0..sizeN form 4+7+7+..+7 bit integer, size0
|
|
is the least significant part, and sizeN is the
|
|
most significant part.
|
|
packed object data:
|
|
If it is not DELTA, then deflated bytes (the size above
|
|
is the size before compression).
|
|
If it is REF_DELTA, then
|
|
20-byte base object name SHA-1 (the size above is the
|
|
size of the delta data that follows).
|
|
delta data, deflated.
|
|
If it is OFS_DELTA, then
|
|
n-byte offset (see below) interpreted as a negative
|
|
offset from the type-byte of the header of the
|
|
ofs-delta entry (the size above is the size of
|
|
the delta data that follows).
|
|
delta data, deflated.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre> offset encoding:
|
|
n bytes with MSB set in all but the last one.
|
|
The offset is then the number constructed by
|
|
concatenating the lower 7 bit of each byte, and
|
|
for n >= 2 adding 2^7 + 2^14 + ... + 2^(7*(n-1))
|
|
to the result.</pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_version_2_pack_idx_files_support_packs_larger_than_4_gib_and">Version 2 pack-*.idx files support packs larger than 4 GiB, and</h2>
|
|
<div class="sectionbody">
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>have some other reorganizations. They have the format:</pre>
|
|
</div>
|
|
</div>
|
|
<div class="ulist">
|
|
<ul>
|
|
<li>
|
|
<p>A 4-byte magic number <em>\377tOc</em> which is an unreasonable
|
|
fanout[0] value.</p>
|
|
</li>
|
|
<li>
|
|
<p>A 4-byte version number (= 2)</p>
|
|
</li>
|
|
<li>
|
|
<p>A 256-entry fan-out table just like v1.</p>
|
|
</li>
|
|
<li>
|
|
<p>A table of sorted 20-byte SHA-1 object names. These are
|
|
packed together without offset values to reduce the cache
|
|
footprint of the binary search for a specific object name.</p>
|
|
</li>
|
|
<li>
|
|
<p>A table of 4-byte CRC32 values of the packed object data.
|
|
This is new in v2 so compressed data can be copied directly
|
|
from pack to pack during repacking without undetected
|
|
data corruption.</p>
|
|
</li>
|
|
<li>
|
|
<p>A table of 4-byte offset values (in network byte order).
|
|
These are usually 31-bit pack file offsets, but large
|
|
offsets are encoded as an index into the next table with
|
|
the msbit set.</p>
|
|
</li>
|
|
<li>
|
|
<p>A table of 8-byte offset entries (empty for pack files less
|
|
than 2 GiB). Pack files are organized with heavily used
|
|
objects toward the front, so most object references should
|
|
not need to refer to this table.</p>
|
|
</li>
|
|
<li>
|
|
<p>The same trailer as a v1 pack file:</p>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>A copy of the 20-byte SHA-1 checksum at the end of
|
|
corresponding packfile.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>20-byte SHA-1-checksum of all of the above.</pre>
|
|
</div>
|
|
</div>
|
|
</li>
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="sect1">
|
|
<h2 id="_multi_pack_index_midx_files_have_the_following_format">multi-pack-index (MIDX) files have the following format:</h2>
|
|
<div class="sectionbody">
|
|
<div class="paragraph">
|
|
<p>The multi-pack-index files refer to multiple pack-files and loose objects.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>In order to allow extensions that add extra data to the MIDX, we organize
|
|
the body into "chunks" and provide a lookup table at the beginning of the
|
|
body. The header includes certain length values, such as the number of packs,
|
|
the number of base MIDX files, hash lengths and types.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>All 4-byte numbers are in network order.</p>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>HEADER:</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>4-byte signature:
|
|
The signature is: {'M', 'I', 'D', 'X'}</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>1-byte version number:
|
|
Git only writes or recognizes version 1.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>1-byte Object Id Version
|
|
Git only writes or recognizes version 1 (SHA1).</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>1-byte number of "chunks"</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>1-byte number of base multi-pack-index files:
|
|
This value is currently always zero.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>4-byte number of pack files</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>CHUNK LOOKUP:</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>(C + 1) * 12 bytes providing the chunk offsets:
|
|
First 4 bytes describe chunk id. Value 0 is a terminating label.
|
|
Other 8 bytes provide offset in current file for chunk to start.
|
|
(Chunks are provided in file-order, so you can infer the length
|
|
using the next chunk position if necessary.)</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>The remaining data in the body is described one chunk at a time, and
|
|
these chunks may be given in any order. Chunks are required unless
|
|
otherwise specified.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>CHUNK DATA:</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>Packfile Names (ID: {'P', 'N', 'A', 'M'})
|
|
Stores the packfile names as concatenated, null-terminated strings.
|
|
Packfiles must be listed in lexicographic order for fast lookups by
|
|
name. This is the only chunk not guaranteed to be a multiple of four
|
|
bytes in length, so should be the last chunk for alignment reasons.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>OID Fanout (ID: {'O', 'I', 'D', 'F'})
|
|
The ith entry, F[i], stores the number of OIDs with first
|
|
byte at most i. Thus F[255] stores the total
|
|
number of objects.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>OID Lookup (ID: {'O', 'I', 'D', 'L'})
|
|
The OIDs for all objects in the MIDX are stored in lexicographic
|
|
order in this chunk.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>Object Offsets (ID: {'O', 'O', 'F', 'F'})
|
|
Stores two 4-byte values for every object.
|
|
1: The pack-int-id for the pack storing this object.
|
|
2: The offset within the pack.
|
|
If all offsets are less than 2^31, then the large offset chunk
|
|
will not exist and offsets are stored as in IDX v1.
|
|
If there is at least one offset value larger than 2^32-1, then
|
|
the large offset chunk must exist. If the large offset chunk
|
|
exists and the 31st bit is on, then removing that bit reveals
|
|
the row in the large offsets containing the 8-byte offset of
|
|
this object.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>[Optional] Object Large Offsets (ID: {'L', 'O', 'F', 'F'})
|
|
8-byte offsets into large packfiles.</pre>
|
|
</div>
|
|
</div>
|
|
<div class="paragraph">
|
|
<p>TRAILER:</p>
|
|
</div>
|
|
<div class="literalblock">
|
|
<div class="content">
|
|
<pre>20-byte SHA1-checksum of the above contents.</pre>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div id="footer">
|
|
<div id="footer-text">
|
|
Last updated 2019-02-26 19:31:11 UTC
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html> |