ref: a3f2d6d23ed1be69fee607bdedadc0438fd01305
dir: /sys/src/libc/amd64/memcpy.s/
TEXT memcpy(SB), $0 MOVQ RARG, DI MOVQ DI, AX /* return value */ MOVQ p2+8(FP), SI MOVQ n+16(FP), BX CMPQ BX, $0 JGT _ok JEQ _return /* nothing to do if n == 0 */ MOVL $0, SI /* fault if n < 0 */ /* * check and set for backwards: * (p2 < p1) && ((p2+n) > p1) */ _ok: CMPQ SI, DI JGT _forward JEQ _return /* nothing to do if p2 == p1 */ MOVQ SI, DX ADDQ BX, DX CMPQ DX, DI JGT _back /* * copy whole longs if aligned */ _forward: CLD MOVQ SI, DX ORQ DI, DX ANDL $3, DX JNE c3f MOVQ BX, CX SHRQ $2, CX ANDL $3, BX REP; MOVSL /* * copy the rest, by bytes */ JEQ _return /* flags set by above ANDL */ c3f: MOVQ BX, CX REP; MOVSB RET /* * whole thing backwards has * adjusted addresses */ _back: ADDQ BX, DI ADDQ BX, SI STD SUBQ $4, DI SUBQ $4, SI /* * copy whole longs, if aligned */ MOVQ DI, DX ORQ SI, DX ANDL $3, DX JNE c3b MOVQ BX, CX SHRQ $2, CX ANDL $3, BX REP; MOVSL /* * copy the rest, by bytes */ JEQ _return /* flags set by above ANDL */ c3b: ADDQ $3, DI ADDQ $3, SI MOVQ BX, CX REP; MOVSB _return: RET