| // Copyright 2009 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| TEXT ·IndexByte(SB),7,$0 |
| MOVQ p+0(FP), SI |
| MOVL len+8(FP), BX |
| MOVB b+16(FP), AL |
| MOVQ SI, DI |
| |
| CMPL BX, $16 |
| JLT small |
| |
| // round up to first 16-byte boundary |
| TESTQ $15, SI |
| JZ aligned |
| MOVQ SI, CX |
| ANDQ $~15, CX |
| ADDQ $16, CX |
| |
| // search the beginning |
| SUBQ SI, CX |
| REPN; SCASB |
| JZ success |
| |
| // DI is 16-byte aligned; get ready to search using SSE instructions |
| aligned: |
| // round down to last 16-byte boundary |
| MOVQ BX, R11 |
| ADDQ SI, R11 |
| ANDQ $~15, R11 |
| |
| // shuffle X0 around so that each byte contains c |
| MOVD AX, X0 |
| PUNPCKLBW X0, X0 |
| PUNPCKLBW X0, X0 |
| PSHUFL $0, X0, X0 |
| JMP condition |
| |
| sse: |
| // move the next 16-byte chunk of the buffer into X1 |
| MOVO (DI), X1 |
| // compare bytes in X0 to X1 |
| PCMPEQB X0, X1 |
| // take the top bit of each byte in X1 and put the result in DX |
| PMOVMSKB X1, DX |
| TESTL DX, DX |
| JNZ ssesuccess |
| ADDQ $16, DI |
| |
| condition: |
| CMPQ DI, R11 |
| JLT sse |
| |
| // search the end |
| MOVQ SI, CX |
| ADDQ BX, CX |
| SUBQ R11, CX |
| // if CX == 0, the zero flag will be set and we'll end up |
| // returning a false success |
| JZ failure |
| REPN; SCASB |
| JZ success |
| |
| failure: |
| MOVL $-1, ret+24(FP) |
| RET |
| |
| // handle for lengths < 16 |
| small: |
| MOVL BX, CX |
| REPN; SCASB |
| JZ success |
| MOVL $-1, ret+24(FP) |
| RET |
| |
| // we've found the chunk containing the byte |
| // now just figure out which specific byte it is |
| ssesuccess: |
| // get the index of the least significant set bit |
| BSFW DX, DX |
| SUBQ SI, DI |
| ADDQ DI, DX |
| MOVL DX, ret+24(FP) |
| RET |
| |
| success: |
| SUBQ SI, DI |
| SUBL $1, DI |
| MOVL DI, ret+24(FP) |
| RET |
| |
