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Diffstat (limited to 'sysdeps/alpha/strlen.S')
| -rw-r--r-- | sysdeps/alpha/strlen.S | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/sysdeps/alpha/strlen.S b/sysdeps/alpha/strlen.S new file mode 100644 index 0000000000..3e55220fad --- /dev/null +++ b/sysdeps/alpha/strlen.S @@ -0,0 +1,76 @@ +/* Copyright (C) 1996-2014 Free Software Foundation, Inc. + Contributed by David Mosberger (davidm@cs.arizona.edu). + 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/>. */ + +/* Finds length of a 0-terminated string. Optimized for the Alpha + architecture: + + - memory accessed as aligned quadwords only + - uses cmpbge to compare 8 bytes in parallel + - does binary search to find 0 byte in last quadword (HAKMEM + needed 12 instructions to do this instead of the 8 instructions + that the binary search needs). +*/ + +#include <sysdep.h> + + .set noreorder + .set noat + +ENTRY(strlen) +#ifdef PROF + ldgp gp, 0(pv) + lda AT, _mcount + jsr AT, (AT), _mcount + .prologue 1 +#else + .prologue 0 +#endif + + ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned) + lda t1, -1(zero) + insqh t1, a0, t1 + andnot a0, 7, v0 + or t1, t0, t0 + nop # dual issue the next two on ev5 + cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0 + bne t1, $found + +$loop: ldq t0, 8(v0) + addq v0, 8, v0 # addr += 8 + cmpbge zero, t0, t1 + beq t1, $loop + +$found: negq t1, t2 # clear all but least set bit + and t1, t2, t1 + + and t1, 0xf0, t2 # binary search for that set bit + and t1, 0xcc, t3 + and t1, 0xaa, t4 + cmovne t2, 4, t2 + cmovne t3, 2, t3 + cmovne t4, 1, t4 + addq t2, t3, t2 + addq v0, t4, v0 + addq v0, t2, v0 + nop # dual issue next two on ev4 and ev5 + + subq v0, a0, v0 + ret + + END(strlen) +libc_hidden_builtin_def (strlen) |