1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/patches/glibc/2.9/210-2.9-strlen-hack.patch Sun Apr 19 16:17:11 2009 +0000
1.3 @@ -0,0 +1,109 @@
1.4 +Original patch from: gentoo/src/patchsets/glibc/2.9/1020_all_glibc-2.9-strlen-hack.patch
1.5 +
1.6 +-= BEGIN original header =-
1.7 +http://sourceware.org/bugzilla/show_bug.cgi?id=5807
1.8 +http://www.cl.cam.ac.uk/~am21/progtricks.html
1.9 +
1.10 +-= END original header =-
1.11 +
1.12 +diff -durN glibc-2_9.orig/string/strlen.c glibc-2_9/string/strlen.c
1.13 +--- glibc-2_9.orig/string/strlen.c 2005-12-14 12:09:07.000000000 +0100
1.14 ++++ glibc-2_9/string/strlen.c 2009-02-02 22:00:51.000000000 +0100
1.15 +@@ -32,7 +32,7 @@
1.16 + {
1.17 + const char *char_ptr;
1.18 + const unsigned long int *longword_ptr;
1.19 +- unsigned long int longword, magic_bits, himagic, lomagic;
1.20 ++ unsigned long int longword, himagic, lomagic;
1.21 +
1.22 + /* Handle the first few characters by reading one character at a time.
1.23 + Do this until CHAR_PTR is aligned on a longword boundary. */
1.24 +@@ -42,28 +42,14 @@
1.25 + if (*char_ptr == '\0')
1.26 + return char_ptr - str;
1.27 +
1.28 +- /* All these elucidatory comments refer to 4-byte longwords,
1.29 +- but the theory applies equally well to 8-byte longwords. */
1.30 +-
1.31 + longword_ptr = (unsigned long int *) char_ptr;
1.32 +
1.33 +- /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits
1.34 +- the "holes." Note that there is a hole just to the left of
1.35 +- each byte, with an extra at the end:
1.36 +-
1.37 +- bits: 01111110 11111110 11111110 11111111
1.38 +- bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD
1.39 +-
1.40 +- The 1-bits make sure that carries propagate to the next 0-bit.
1.41 +- The 0-bits provide holes for carries to fall into. */
1.42 +- magic_bits = 0x7efefeffL;
1.43 + himagic = 0x80808080L;
1.44 + lomagic = 0x01010101L;
1.45 + if (sizeof (longword) > 4)
1.46 + {
1.47 + /* 64-bit version of the magic. */
1.48 + /* Do the shift in two steps to avoid a warning if long has 32 bits. */
1.49 +- magic_bits = ((0x7efefefeL << 16) << 16) | 0xfefefeffL;
1.50 + himagic = ((himagic << 16) << 16) | himagic;
1.51 + lomagic = ((lomagic << 16) << 16) | lomagic;
1.52 + }
1.53 +@@ -75,56 +61,12 @@
1.54 + if *any of the four* bytes in the longword in question are zero. */
1.55 + for (;;)
1.56 + {
1.57 +- /* We tentatively exit the loop if adding MAGIC_BITS to
1.58 +- LONGWORD fails to change any of the hole bits of LONGWORD.
1.59 +-
1.60 +- 1) Is this safe? Will it catch all the zero bytes?
1.61 +- Suppose there is a byte with all zeros. Any carry bits
1.62 +- propagating from its left will fall into the hole at its
1.63 +- least significant bit and stop. Since there will be no
1.64 +- carry from its most significant bit, the LSB of the
1.65 +- byte to the left will be unchanged, and the zero will be
1.66 +- detected.
1.67 +-
1.68 +- 2) Is this worthwhile? Will it ignore everything except
1.69 +- zero bytes? Suppose every byte of LONGWORD has a bit set
1.70 +- somewhere. There will be a carry into bit 8. If bit 8
1.71 +- is set, this will carry into bit 16. If bit 8 is clear,
1.72 +- one of bits 9-15 must be set, so there will be a carry
1.73 +- into bit 16. Similarly, there will be a carry into bit
1.74 +- 24. If one of bits 24-30 is set, there will be a carry
1.75 +- into bit 31, so all of the hole bits will be changed.
1.76 +-
1.77 +- The one misfire occurs when bits 24-30 are clear and bit
1.78 +- 31 is set; in this case, the hole at bit 31 is not
1.79 +- changed. If we had access to the processor carry flag,
1.80 +- we could close this loophole by putting the fourth hole
1.81 +- at bit 32!
1.82 +-
1.83 +- So it ignores everything except 128's, when they're aligned
1.84 +- properly. */
1.85 +-
1.86 + longword = *longword_ptr++;
1.87 +
1.88 +- if (
1.89 +-#if 0
1.90 +- /* Add MAGIC_BITS to LONGWORD. */
1.91 +- (((longword + magic_bits)
1.92 +-
1.93 +- /* Set those bits that were unchanged by the addition. */
1.94 +- ^ ~longword)
1.95 +-
1.96 +- /* Look at only the hole bits. If any of the hole bits
1.97 +- are unchanged, most likely one of the bytes was a
1.98 +- zero. */
1.99 +- & ~magic_bits)
1.100 +-#else
1.101 +- ((longword - lomagic) & himagic)
1.102 +-#endif
1.103 +- != 0)
1.104 ++ /* This hack taken from Alan Mycroft's HAKMEMC postings.
1.105 ++ See: http://www.cl.cam.ac.uk/~am21/progtricks.html */
1.106 ++ if (((longword - lomagic) & ~longword & himagic) != 0)
1.107 + {
1.108 +- /* Which of the bytes was the zero? If none of them were, it was
1.109 +- a misfire; continue the search. */
1.110 +
1.111 + const char *cp = (const char *) (longword_ptr - 1);
1.112 +