| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* Copyright (C) 1996-2015 Free Software Foundation, Inc. |
| 2 | Contributed by David Mosberger (davidm@cs.arizona.edu). |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 of the License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library. If not, see |
| 17 | <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | /* Finds length of a 0-terminated string. Optimized for the Alpha |
| 20 | architecture: |
| 21 | |
| 22 | - memory accessed as aligned quadwords only |
| 23 | - uses cmpbge to compare 8 bytes in parallel |
| 24 | - does binary search to find 0 byte in last quadword (HAKMEM |
| 25 | needed 12 instructions to do this instead of the 8 instructions |
| 26 | that the binary search needs). |
| 27 | */ |
| 28 | |
| 29 | #include <sysdep.h> |
| 30 | |
| 31 | .set noreorder |
| 32 | .set noat |
| 33 | |
| 34 | ENTRY(strlen) |
| 35 | #ifdef PROF |
| 36 | ldgp gp, 0(pv) |
| 37 | lda AT, _mcount |
| 38 | jsr AT, (AT), _mcount |
| 39 | .prologue 1 |
| 40 | #else |
| 41 | .prologue 0 |
| 42 | #endif |
| 43 | |
| 44 | ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned) |
| 45 | lda t1, -1(zero) |
| 46 | insqh t1, a0, t1 |
| 47 | andnot a0, 7, v0 |
| 48 | or t1, t0, t0 |
| 49 | nop # dual issue the next two on ev5 |
| 50 | cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0 |
| 51 | bne t1, $found |
| 52 | |
| 53 | $loop: ldq t0, 8(v0) |
| 54 | addq v0, 8, v0 # addr += 8 |
| 55 | cmpbge zero, t0, t1 |
| 56 | beq t1, $loop |
| 57 | |
| 58 | $found: negq t1, t2 # clear all but least set bit |
| 59 | and t1, t2, t1 |
| 60 | |
| 61 | and t1, 0xf0, t2 # binary search for that set bit |
| 62 | and t1, 0xcc, t3 |
| 63 | and t1, 0xaa, t4 |
| 64 | cmovne t2, 4, t2 |
| 65 | cmovne t3, 2, t3 |
| 66 | cmovne t4, 1, t4 |
| 67 | addq t2, t3, t2 |
| 68 | addq v0, t4, v0 |
| 69 | addq v0, t2, v0 |
| 70 | nop # dual issue next two on ev4 and ev5 |
| 71 | |
| 72 | subq v0, a0, v0 |
| 73 | ret |
| 74 | |
| 75 | END(strlen) |
| 76 | libc_hidden_builtin_def (strlen) |