From 4bec0ef03e91506caf60d8842786b29c2d2ff049 Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Mon, 28 Dec 2015 22:00:14 +0000 Subject: [PATCH] libiberty: Tweak the documentation of libiberty's xcrc32 function In some places the xcrc32 documentation refers to GDB's own crc32 implementation, but GDB no longer has its own crc32 implementation. It now uses libiberty's xcrc32 throughout. So this patch removes these references to GDB's now-nonexistent crc32 implementation. Also, there appears to be a bug in the table-generation program embedded within the documentation. When the variable "int i" is >= 128, the computation "i << 24" shifts a one bit into the sign bit (assuming a 32-bit int), which is UB. To avoid this UB, I think it is sufficient to make the induction variables i and j have type unsigned int. This bug seems latent, however. I ran the program before and after this change and the table output is the same. --- libiberty/ChangeLog | 8 ++++++++ libiberty/crc32.c | 12 +++++------- 2 files changed, 13 insertions(+), 7 deletions(-) diff --git a/libiberty/ChangeLog b/libiberty/ChangeLog index e8fc96acb5..aa598f277b 100644 --- a/libiberty/ChangeLog +++ b/libiberty/ChangeLog @@ -1,3 +1,11 @@ +2015-12-28 Patrick Palka + + * crc32.c: In the documentation, don't refer to GDB's + now-nonexistent crc32 implementation. In the table-generation + program embedded within the documentation, change the type of + the induction variables i and j from int to unsigned int, to + avoid undefined behavior. + 2015-12-21 Nick Clifton PR 66827 diff --git a/libiberty/crc32.c b/libiberty/crc32.c index 12d9be07cf..52c982fb58 100644 --- a/libiberty/crc32.c +++ b/libiberty/crc32.c @@ -33,15 +33,14 @@ #include "libiberty.h" -/* This table was generated by the following program. This matches - what gdb does. +/* This table was generated by the following program. #include int main () { - int i, j; + unsigned int i, j; unsigned int c; int table[256]; @@ -146,10 +145,9 @@ starting value is @var{init}; this may be used to compute the CRC of data split across multiple buffers by passing the return value of each call as the @var{init} parameter of the next. -This is intended to match the CRC used by the @command{gdb} remote -protocol for the @samp{qCRC} command. In order to get the same -results as gdb for a block of data, you must pass the first CRC -parameter as @code{0xffffffff}. +This is used by the @command{gdb} remote protocol for the @samp{qCRC} +command. In order to get the same results as gdb for a block of data, +you must pass the first CRC parameter as @code{0xffffffff}. This CRC can be specified as: