1.1 --- a/patches/glibc/2_9/210-2.9-strlen-hack.patch Sat Apr 11 19:03:02 2009 +0000
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,109 +0,0 @@
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 -