[FFmpeg-devel] [PATCH] md5: consistently use uint32_t instead of unsigned int
michaelni at gmx.at
Sat Jun 16 12:49:55 CEST 2012
On Fri, Jun 15, 2012 at 09:14:40PM +0200, Giorgio Vazzana wrote:
> 2012/6/15 Michael Niedermayer <michaelni at gmx.at>:
> > On Fri, Jun 15, 2012 at 06:03:12PM +0200, Giorgio Vazzana wrote:
> >> As in subject, 'make fate' passes, please review.
> > [...]
> >> md5.c | 10 +++++-----
> >> 1 file changed, 5 insertions(+), 5 deletions(-)
> >> 8cb92a43c030e7c1e82de36b8e7e6ded7b42bf4d 0001-md5-consistently-use-uint32_t-instead-of-unsigned-in.patch
> >> From 48bb8ff622713ede5b978fce6cf81c39d8a2131d Mon Sep 17 00:00:00 2001
> >> From: Giorgio Vazzana <mywing81 at gmail.com>
> >> Date: Fri, 15 Jun 2012 17:21:36 +0200
> >> Subject: [PATCH] md5: consistently use uint32_t instead of unsigned int
> > can you explain why you change unsigned int to uint32_t, is this
> > fixing a bug or some warnings or ?
> Yes, sorry. Basically to make code clearer and adherent to the
> standard. RFC 1321, on page 2 states
> Let the symbol "+" denote addition of words (i.e., modulo-2^32
> addition). Let X <<< s denote the 32-bit value obtained by circularly
> shifting (rotating) X left by s bit positions.
> on page 3, section 3.3 states:
> A four-word buffer (A,B,C,D) is used to compute the message digest.
> Here each of A, B, C, D is a 32-bit register.
> so the algorithm needs to work with integers that are exactly 32bits
> in length. And indeed in struct AVMD5 the MD buffer is declared as
> "uint32_t ABCD;", while in the function that performs the block
> transformation the state variables were "unsigned int"s. On
> architectures where sizeof(unsigned int) != sizeof(uint32_t) this
> could be a problem, although I can't name such an architecture from
> the top of my head.
> On a side note, both the reference implementation in RFC 1321 and the
> gnulib implementation (used by md5sum program on GNU systems) use
> uint32_t in the transform function.
i can confirm that the code doesnt work with 64bit abcd variables
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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