-
-
Save hackape/8c4c2fa88b6623cdd0aaca1005d5496f to your computer and use it in GitHub Desktop.
Revisions
-
masak revised this gist
Oct 18, 2021 . 1 changed file with 4 additions and 4 deletions.There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -13,7 +13,7 @@ So that's the sha1 I want to reproduce. `d6cd1e2bd19e03a81132a23b2025920577f84e3 When I started my investigations, I *thought* it was something like these things that went into a commit: $ git --no-replace-objects cat-file commit HEAD tree 9bedf67800b2923982bdf60c89c57ce6fd2d9a1c parent de1eaf515ebea46dedea7b3ae0e5ebe3e1818971 author jnthn <[email protected]> 1334500503 +0200 @@ -31,14 +31,14 @@ That is But it turns out there is also a NUL-terminated header that gets appended to this, containing the word "commit", and the length in bytes of all of the above information: $ printf "commit %s\0" $(git --no-replace-objects cat-file commit HEAD | wc -c) commit 327 (No, you can't see the NUL byte.) Put this header and the rest of the information together: $ (printf "commit %s\0" $(git --no-replace-objects cat-file commit HEAD | wc -c); git cat-file commit HEAD) commit 327tree 9bedf67800b2923982bdf60c89c57ce6fd2d9a1c parent de1eaf515ebea46dedea7b3ae0e5ebe3e1818971 author jnthn <[email protected]> 1334500503 +0200 @@ -48,5 +48,5 @@ Put this header and the rest of the information together: ...and what you get hashes to the right sha1! $ (printf "commit %s\0" $(git --no-replace-objects cat-file commit HEAD | wc -c); git cat-file commit HEAD) | sha1sum d6cd1e2bd19e03a81132a23b2025920577f84e37 - -
Carl Mäsak created this gist
Apr 18, 2012 .There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters. Learn more about bidirectional Unicode charactersOriginal file line number Diff line number Diff line change @@ -0,0 +1,52 @@ Ok, I geeked out, and this is probably more information than you need. But it *completely* answers the question. Sorry. ☺ Locally, I'm at this commit: $ git show commit d6cd1e2bd19e03a81132a23b2025920577f84e37 Author: jnthn <[email protected]> Date: Sun Apr 15 16:35:03 2012 +0200 When I added FIRST/NEXT/LAST, it was idiomatic but not quite so fast. This makes it faster. Another little bit of masak++'s program. So that's the sha1 I want to reproduce. `d6cd1e2bd19e03a81132a23b2025920577f84e37` When I started my investigations, I *thought* it was something like these things that went into a commit: $ git cat-file commit HEAD tree 9bedf67800b2923982bdf60c89c57ce6fd2d9a1c parent de1eaf515ebea46dedea7b3ae0e5ebe3e1818971 author jnthn <[email protected]> 1334500503 +0200 committer jnthn <[email protected]> 1334500545 +0200 When I added FIRST/NEXT/LAST, it was idiomatic but not quite so fast. This makes it faster. Another little bit of masak++'s program. That is * The source tree of the commit (which unravels to all the subtrees and blobs) * The parent commit sha1 * The author info * The committer info (right, those are different!) * The commit message But it turns out there is also a NUL-terminated header that gets appended to this, containing the word "commit", and the length in bytes of all of the above information: $ printf "commit %s\0" $(git cat-file commit HEAD | wc -c) commit 327 (No, you can't see the NUL byte.) Put this header and the rest of the information together: $ (printf "commit %s\0" $(git cat-file commit HEAD | wc -c); git cat-file commit HEAD) commit 327tree 9bedf67800b2923982bdf60c89c57ce6fd2d9a1c parent de1eaf515ebea46dedea7b3ae0e5ebe3e1818971 author jnthn <[email protected]> 1334500503 +0200 committer jnthn <[email protected]> 1334500545 +0200 When I added FIRST/NEXT/LAST, it was idiomatic but not quite so fast. This makes it faster. Another little bit of masak++'s program. ...and what you get hashes to the right sha1! $ (printf "commit %s\0" $(git cat-file commit HEAD | wc -c); git cat-file commit HEAD) | sha1sum d6cd1e2bd19e03a81132a23b2025920577f84e37 -
Carl Mäsak
created
this gist