1 /* Copyright (C) 1996-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library. If not, see
16 <https://www.gnu.org/licenses/>. */
18 /* Finds length of a 0-terminated string. Optimized for the Alpha
21 - memory accessed as aligned quadwords only
22 - uses cmpbge to compare 8 bytes in parallel
23 - does binary search to find 0 byte in last quadword (HAKMEM
24 needed 12 instructions to do this instead of the 8 instructions
25 that the binary search needs).
43 ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned)
48 nop # dual issue the next two on ev5
49 cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0
53 addq v0, 8, v0 # addr += 8
57 $found: negq t1, t2 # clear all but least set bit
60 and t1, 0xf0, t2 # binary search for that set bit
69 nop # dual issue next two on ev4 and ev5
75 libc_hidden_builtin_def (strlen)