diff options
Diffstat (limited to 'patches/glibc/2_9/210-2.9-strlen-hack.patch')
| -rw-r--r-- | patches/glibc/2_9/210-2.9-strlen-hack.patch | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/patches/glibc/2_9/210-2.9-strlen-hack.patch b/patches/glibc/2_9/210-2.9-strlen-hack.patch new file mode 100644 index 0000000..6071724 --- /dev/null +++ b/patches/glibc/2_9/210-2.9-strlen-hack.patch @@ -0,0 +1,109 @@ +Original patch from: gentoo/src/patchsets/glibc/2.9/1020_all_glibc-2.9-strlen-hack.patch + +-= BEGIN original header =- +http://sourceware.org/bugzilla/show_bug.cgi?id=5807 +http://www.cl.cam.ac.uk/~am21/progtricks.html + +-= END original header =- + +diff -durN glibc-2_9.orig/string/strlen.c glibc-2_9/string/strlen.c +--- glibc-2_9.orig/string/strlen.c 2005-12-14 12:09:07.000000000 +0100 ++++ glibc-2_9/string/strlen.c 2009-02-02 22:00:51.000000000 +0100 +@@ -32,7 +32,7 @@ + { + const char *char_ptr; + const unsigned long int *longword_ptr; +- unsigned long int longword, magic_bits, himagic, lomagic; ++ unsigned long int longword, himagic, lomagic; + + /* Handle the first few characters by reading one character at a time. + Do this until CHAR_PTR is aligned on a longword boundary. */ +@@ -42,28 +42,14 @@ + if (*char_ptr == '\0') + return char_ptr - str; + +- /* All these elucidatory comments refer to 4-byte longwords, +- but the theory applies equally well to 8-byte longwords. */ +- + longword_ptr = (unsigned long int *) char_ptr; + +- /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits +- the "holes." Note that there is a hole just to the left of +- each byte, with an extra at the end: +- +- bits: 01111110 11111110 11111110 11111111 +- bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD +- +- The 1-bits make sure that carries propagate to the next 0-bit. +- The 0-bits provide holes for carries to fall into. */ +- magic_bits = 0x7efefeffL; + himagic = 0x80808080L; + lomagic = 0x01010101L; + if (sizeof (longword) > 4) + { + /* 64-bit version of the magic. */ + /* Do the shift in two steps to avoid a warning if long has 32 bits. */ +- magic_bits = ((0x7efefefeL << 16) << 16) | 0xfefefeffL; + himagic = ((himagic << 16) << 16) | himagic; + lomagic = ((lomagic << 16) << 16) | lomagic; + } +@@ -75,56 +61,12 @@ + if *any of the four* bytes in the longword in question are zero. */ + for (;;) + { +- /* We tentatively exit the loop if adding MAGIC_BITS to +- LONGWORD fails to change any of the hole bits of LONGWORD. +- +- 1) Is this safe? Will it catch all the zero bytes? +- Suppose there is a byte with all zeros. Any carry bits +- propagating from its left will fall into the hole at its +- least significant bit and stop. Since there will be no +- carry from its most significant bit, the LSB of the +- byte to the left will be unchanged, and the zero will be +- detected. +- +- 2) Is this worthwhile? Will it ignore everything except +- zero bytes? Suppose every byte of LONGWORD has a bit set +- somewhere. There will be a carry into bit 8. If bit 8 +- is set, this will carry into bit 16. If bit 8 is clear, +- one of bits 9-15 must be set, so there will be a carry +- into bit 16. Similarly, there will be a carry into bit +- 24. If one of bits 24-30 is set, there will be a carry +- into bit 31, so all of the hole bits will be changed. +- +- The one misfire occurs when bits 24-30 are clear and bit +- 31 is set; in this case, the hole at bit 31 is not +- changed. If we had access to the processor carry flag, +- we could close this loophole by putting the fourth hole +- at bit 32! +- +- So it ignores everything except 128's, when they're aligned +- properly. */ +- + longword = *longword_ptr++; + +- if ( +-#if 0 +- /* Add MAGIC_BITS to LONGWORD. */ +- (((longword + magic_bits) +- +- /* Set those bits that were unchanged by the addition. */ +- ^ ~longword) +- +- /* Look at only the hole bits. If any of the hole bits +- are unchanged, most likely one of the bytes was a +- zero. */ +- & ~magic_bits) +-#else +- ((longword - lomagic) & himagic) +-#endif +- != 0) ++ /* This hack taken from Alan Mycroft's HAKMEMC postings. ++ See: http://www.cl.cam.ac.uk/~am21/progtricks.html */ ++ if (((longword - lomagic) & ~longword & himagic) != 0) + { +- /* Which of the bytes was the zero? If none of them were, it was +- a misfire; continue the search. */ + + const char *cp = (const char *) (longword_ptr - 1); + |