diff options
Diffstat (limited to 'sysdeps/alpha/memchr.c')
| -rw-r--r-- | sysdeps/alpha/memchr.c | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/sysdeps/alpha/memchr.c b/sysdeps/alpha/memchr.c new file mode 100644 index 0000000000..6d80690b1d --- /dev/null +++ b/sysdeps/alpha/memchr.c @@ -0,0 +1,174 @@ +/* Copyright (C) 2010-2014 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library. If not, see + <http://www.gnu.org/licenses/>. */ + +#include <string.h> + +typedef unsigned long word; + +static inline word +ldq_u(const void *s) +{ + return *(const word *)((word)s & -8); +} + +#define unlikely(X) __builtin_expect ((X), 0) +#define prefetch(X) __builtin_prefetch ((void *)(X), 0) + +#define cmpbeq0(X) __builtin_alpha_cmpbge(0, (X)) +#define find(X, Y) cmpbeq0 ((X) ^ (Y)) + +/* Search no more than N bytes of S for C. */ + +void * +__memchr (const void *s, int xc, size_t n) +{ + const word *s_align; + word t, current, found, mask, offset; + + if (unlikely (n == 0)) + return 0; + + current = ldq_u (s); + + /* Replicate low byte of XC into all bytes of C. */ + t = xc & 0xff; /* 0000000c */ + t = (t << 8) | t; /* 000000cc */ + t = (t << 16) | t; /* 0000cccc */ + const word c = (t << 32) | t; /* cccccccc */ + + /* Align the source, and decrement the count by the number + of bytes searched in the first word. */ + s_align = (const word *)((word)s & -8); + n += ((word)s & 7); + + /* Deal with misalignment in the first word for the comparison. */ + mask = (1ul << ((word)s & 7)) - 1; + + /* If the entire string fits within one word, we may need masking + at both the front and the back of the string. */ + if (unlikely (n <= 8)) + { + mask |= -1ul << n; + goto last_quad; + } + + found = find (current, c) & ~mask; + if (unlikely (found)) + goto found_it; + + s_align++; + n -= 8; + + /* If the block is sufficiently large, align to cacheline and prefetch. */ + if (unlikely (n >= 256)) + { + /* Prefetch 3 cache lines beyond the one we're working on. */ + prefetch (s_align + 8); + prefetch (s_align + 16); + prefetch (s_align + 24); + + while ((word)s_align & 63) + { + current = *s_align; + found = find (current, c); + if (found) + goto found_it; + s_align++; + n -= 8; + } + + /* Within each cacheline, advance the load for the next word + before the test for the previous word is complete. This + allows us to hide the 3 cycle L1 cache load latency. We + only perform this advance load within a cacheline to prevent + reading across page boundary. */ +#define CACHELINE_LOOP \ + do { \ + word i, next = s_align[0]; \ + for (i = 0; i < 7; ++i) \ + { \ + current = next; \ + next = s_align[1]; \ + found = find (current, c); \ + if (unlikely (found)) \ + goto found_it; \ + s_align++; \ + } \ + current = next; \ + found = find (current, c); \ + if (unlikely (found)) \ + goto found_it; \ + s_align++; \ + n -= 64; \ + } while (0) + + /* While there's still lots more data to potentially be read, + continue issuing prefetches for the 4th cacheline out. */ + while (n >= 256) + { + prefetch (s_align + 24); + CACHELINE_LOOP; + } + + /* Up to 3 cache lines remaining. Continue issuing advanced + loads, but stop prefetching. */ + while (n >= 64) + CACHELINE_LOOP; + + /* We may have exhausted the buffer. */ + if (n == 0) + return NULL; + } + + /* Quadword aligned loop. */ + current = *s_align; + while (n > 8) + { + found = find (current, c); + if (unlikely (found)) + goto found_it; + current = *++s_align; + n -= 8; + } + + /* The last word may need masking at the tail of the compare. */ + mask = -1ul << n; + last_quad: + found = find (current, c) & ~mask; + if (found == 0) + return NULL; + + found_it: +#ifdef __alpha_cix__ + offset = __builtin_alpha_cttz (found); +#else + /* Extract LSB. */ + found &= -found; + + /* Binary search for the LSB. */ + offset = (found & 0x0f ? 0 : 4); + offset += (found & 0x33 ? 0 : 2); + offset += (found & 0x55 ? 0 : 1); +#endif + + return (void *)((word)s_align + offset); +} + +#ifdef weak_alias +weak_alias (__memchr, memchr) +#endif +libc_hidden_builtin_def (memchr) |