# [PATCH] Add description of OFS_DELTA to the pack format description 6 messages from 2008-04-06 to 2008-04-06. Participants: Peter Eriksen, Shawn O. Pearce. Thread: https://gitlist.dev/t/13001 ## Peter Eriksen, 2008-04-06 13:47 Subject: [PATCH] Add description of OFS_DELTA to the pack format description Message-ID: <20080406134739.GA29815@bohr.gbar.dtu.dk> URL: https://gitlist.dev/e/20080406134739.GA29815%40bohr.gbar.dtu.dk ``` Signed-off-by: Peter Eriksen --- I'll take it in smaller steps this time. Documentation/technical/pack-format.txt | 12 +++++++++++- 1 files changed, 11 insertions(+), 1 deletions(-) diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index aa87756..f6b1405 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -103,10 +103,20 @@ Pack file entry: <+ packed object data: If it is not DELTA, then deflated bytes (the size above is the size before compression). - If it is DELTA, then + If it is REF_DELTA, then 20-byte base object name SHA1 (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) (the size above is the + size of the delta data that follows). + delta data, deflated. + + 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 + adding 2^7 + 2^14 + ... + 2^(7*(n-1)) to the result. = Version 2 pack-*.idx files support packs larger than 4 GiB, and -- 1.5.5-rc3.GIT ``` ## Shawn O. Pearce, 2008-04-06 19:07 Subject: Re: [PATCH] Add description of OFS_DELTA to the pack format description Message-ID: <20080406190724.GG10274@spearce.org> URL: https://gitlist.dev/e/20080406190724.GG10274%40spearce.org In-Reply-To: <20080406134739.GA29815@bohr.gbar.dtu.dk> ``` Peter Eriksen wrote: > diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt > index aa87756..f6b1405 100644 > --- a/Documentation/technical/pack-format.txt > +++ b/Documentation/technical/pack-format.txt > @@ -103,10 +103,20 @@ Pack file entry: <+ > packed object data: > If it is not DELTA, then deflated bytes (the size above > is the size before compression). > - If it is DELTA, then > + If it is REF_DELTA, then > 20-byte base object name SHA1 (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) (the size above is the > + size of the delta data that follows). > + delta data, deflated. You are missing the description that the position within _this_ packfile is determined by: offset_of_type_byte - n_byte_offset The above can still be taken to mean the offset is from the start of the packfile or something like that. > + 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 > + adding 2^7 + 2^14 + ... + 2^(7*(n-1)) to the result. Hmm. I've just spent 5 minutes reading this and I'm still not certain what the result is. 2^0 only gets added to the result if there is at least 2 bytes of data in the offset encoding; in your description above it sounds like we should add 2^0 (1) even when there is only 1 offset byte (n=1), which is not correct. -- Shawn. ``` ## Peter Eriksen, 2008-04-06 20:19 Subject: [PATCH v2] Add description of OFS_DELTA to the pack format description Message-ID: <20080406201907.GB7075@bohr.gbar.dtu.dk> URL: https://gitlist.dev/e/20080406201907.GB7075%40bohr.gbar.dtu.dk In-Reply-To: <20080406190724.GG10274@spearce.org> ``` Signed-off-by: Peter Eriksen --- Documentation/technical/pack-format.txt | 16 +++++++++++++++- 1 files changed, 15 insertions(+), 1 deletions(-) On Sun, Apr 06, 2008 at 03:07:24PM -0400, Shawn O. Pearce wrote: ... > You are missing the description that the position within _this_ > packfile is determined by: > > offset_of_type_byte - n_byte_offset > > The above can still be taken to mean the offset is from the start > of the packfile or something like that. Yes, I misunderstood that. Peter diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index aa87756..953c7ee 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -103,10 +103,24 @@ Pack file entry: <+ packed object data: If it is not DELTA, then deflated bytes (the size above is the size before compression). - If it is DELTA, then + If it is REF_DELTA, then 20-byte base object name SHA1 (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) counted 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. + + 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. + = Version 2 pack-*.idx files support packs larger than 4 GiB, and -- 1.5.5-rc3.GIT ``` ## Shawn O. Pearce, 2008-04-06 20:28 Subject: Re: [PATCH v2] Add description of OFS_DELTA to the pack format description Message-ID: <20080406202821.GN10274@spearce.org> URL: https://gitlist.dev/e/20080406202821.GN10274%40spearce.org In-Reply-To: <20080406201907.GB7075@bohr.gbar.dtu.dk> ``` Peter Eriksen wrote: > > diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt > index aa87756..953c7ee 100644 > --- a/Documentation/technical/pack-format.txt > +++ b/Documentation/technical/pack-format.txt > @@ -103,10 +103,24 @@ Pack file entry: <+ > packed object data: > If it is not DELTA, then deflated bytes (the size above > is the size before compression). > - If it is DELTA, then > + If it is REF_DELTA, then > 20-byte base object name SHA1 (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) counted from the type-byte > + of the header of the ofs-delta entry. Except that only a positive offset value is here, as it is always a treated as a negative offset (you can only refer to a base that was before you, as that is the only way to know the base's offset in the pack). > + (the size above is the size of the delta data > + that follows). > + delta data, deflated. > + > + 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. Yes, that sounds correct. -- Shawn. ``` ## Peter Eriksen, 2008-04-06 20:51 Subject: [PATCH v3] Add description of OFS_DELTA to the pack format description Message-ID: <20080406205149.GD7075@bohr.gbar.dtu.dk> URL: https://gitlist.dev/e/20080406205149.GD7075%40bohr.gbar.dtu.dk In-Reply-To: <20080406202821.GN10274@spearce.org> ``` Signed-off-by: Peter Eriksen --- Documentation/technical/pack-format.txt | 16 +++++++++++++++- 1 files changed, 15 insertions(+), 1 deletions(-) diff --git a/Documentation/technical/pack-format.txt b/Documentation/technical/pack-format.txt index aa87756..6b2170f 100644 --- a/Documentation/technical/pack-format.txt +++ b/Documentation/technical/pack-format.txt @@ -103,10 +103,24 @@ Pack file entry: <+ packed object data: If it is not DELTA, then deflated bytes (the size above is the size before compression). - If it is DELTA, then + If it is REF_DELTA, then 20-byte base object name SHA1 (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. + + 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. + = Version 2 pack-*.idx files support packs larger than 4 GiB, and -- 1.5.5-rc3.GIT ``` ## Shawn O. Pearce, 2008-04-06 22:26 Subject: Re: [PATCH v3] Add description of OFS_DELTA to the pack format description Message-ID: <20080406222636.GP10274@spearce.org> URL: https://gitlist.dev/e/20080406222636.GP10274%40spearce.org In-Reply-To: <20080406205149.GD7075@bohr.gbar.dtu.dk> ``` Peter Eriksen wrote: > - If it is DELTA, then > + If it is REF_DELTA, then > 20-byte base object name SHA1 (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. > + > + 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. > + Yup. :-) Acked-by: Shawn O. Pearce -- Shawn. ```