1 /* Copyright (C) 1996 Free Software Foundation, Inc.
2 Contributed by David Mosberger (davidm@cs.arizona.edu).
4 This file is part of the GNU C Library.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Library General Public License as
8 published by the Free Software Foundation; either version 2 of the
9 License, or (at your option) any later version.
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Library General Public License for more details.
16 You should have received a copy of the GNU Library General Public
17 License along with the GNU C Library; see the file COPYING.LIB. If
18 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
19 Cambridge, MA 02139, USA. */
21 /* Finds length of a 0-terminated string. Optimized for the Alpha
24 - memory accessed as aligned quadwords only
25 - uses cmpbge to compare 8 bytes in parallel
26 - does binary search to find 0 byte in last quadword (HAKMEM
27 needed 12 instructions to do this instead of the 8 instructions
28 that the binary search needs).
46 ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned)
51 nop # dual issue the next two on ev5
52 cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0
56 addq v0, 8, v0 # addr += 8
60 $found: negq t1, t2 # clear all but least set bit
63 and t1, 0xf0, t2 # binary search for that set bit
72 nop # dual issue next two on ev4 and ev5