| 1 | /* Copyright (C) 1996-2022 Free Software Foundation, Inc. |
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| 2 | This file is part of the GNU C Library. |
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| 3 | |
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| 4 | The GNU C Library is free software; you can redistribute it and/or |
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| 5 | modify it under the terms of the GNU Lesser General Public |
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| 6 | License as published by the Free Software Foundation; either |
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| 7 | version 2.1 of the License, or (at your option) any later version. |
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| 8 | |
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| 9 | The GNU C Library is distributed in the hope that it will be useful, |
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 12 | Lesser General Public License for more details. |
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| 13 | |
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| 14 | You should have received a copy of the GNU Lesser General Public |
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| 15 | License along with the GNU C Library. If not, see |
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| 16 | <https://www.gnu.org/licenses/>. */ |
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| 17 | |
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| 18 | /* Finds length of a 0-terminated string. Optimized for the Alpha |
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| 19 | architecture: |
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| 20 | |
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| 21 | - memory accessed as aligned quadwords only |
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| 22 | - uses cmpbge to compare 8 bytes in parallel |
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| 23 | - does binary search to find 0 byte in last quadword (HAKMEM |
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| 24 | needed 12 instructions to do this instead of the 8 instructions |
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| 25 | that the binary search needs). |
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| 26 | */ |
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| 27 | |
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| 28 | #include <sysdep.h> |
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| 29 | |
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| 30 | .set noreorder |
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| 31 | .set noat |
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| 32 | |
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| 33 | ENTRY(strlen) |
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| 34 | #ifdef PROF |
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| 35 | ldgp gp, 0(pv) |
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| 36 | lda AT, _mcount |
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| 37 | jsr AT, (AT), _mcount |
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| 38 | .prologue 1 |
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| 39 | #else |
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| 40 | .prologue 0 |
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| 41 | #endif |
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| 42 | |
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| 43 | ldq_u t0, 0(a0) # load first quadword (a0 may be misaligned) |
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| 44 | lda t1, -1(zero) |
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| 45 | insqh t1, a0, t1 |
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| 46 | andnot a0, 7, v0 |
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| 47 | or t1, t0, t0 |
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| 48 | nop # dual issue the next two on ev5 |
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| 49 | cmpbge zero, t0, t1 # t1 <- bitmask: bit i == 1 <==> i-th byte == 0 |
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| 50 | bne t1, $found |
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| 51 | |
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| 52 | $loop: ldq t0, 8(v0) |
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| 53 | addq v0, 8, v0 # addr += 8 |
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| 54 | cmpbge zero, t0, t1 |
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| 55 | beq t1, $loop |
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| 56 | |
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| 57 | $found: negq t1, t2 # clear all but least set bit |
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| 58 | and t1, t2, t1 |
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| 59 | |
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| 60 | and t1, 0xf0, t2 # binary search for that set bit |
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| 61 | and t1, 0xcc, t3 |
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| 62 | and t1, 0xaa, t4 |
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| 63 | cmovne t2, 4, t2 |
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| 64 | cmovne t3, 2, t3 |
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| 65 | cmovne t4, 1, t4 |
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| 66 | addq t2, t3, t2 |
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| 67 | addq v0, t4, v0 |
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| 68 | addq v0, t2, v0 |
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| 69 | nop # dual issue next two on ev4 and ev5 |
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| 70 | |
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| 71 | subq v0, a0, v0 |
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| 72 | ret |
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| 73 | |
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| 74 | END(strlen) |
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| 75 | libc_hidden_builtin_def (strlen) |
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| 76 | |
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