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.

diff --git a/libiberty/ChangeLog b/libiberty/ChangeLog
index e8fc96acb5b54a289dff8acb84da86d1a7fd0f72..aa598f277b2bd39943d887f8117ad6714601b3e6 100644 (file)
--- a/libiberty/ChangeLog
+++ b/libiberty/ChangeLog
@@ -1,3 +1,11 @@
+2015-12-28  Patrick Palka  <ppalka@gcc.gnu.org>
+
+       * 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  <nickc@redhat.com>
 
        PR 66827

diff --git a/libiberty/crc32.c b/libiberty/crc32.c
index 12d9be07cfd65d479aa01e92e2fc6dd8c29509b4..52c982fb58327c0a7b2970d1126684da04dd71ba 100644 (file)
--- 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 <stdio.h>
 
    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: