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// +build sse
// +build amd64
#include "textflag.h"
// func subAsm(a, b []float64)
TEXT ·subAsm(SB), NOSPLIT, $0
MOVQ a_data+0(FP), SI
MOVQ b_data+24(FP), DI // use destination index register for this
MOVQ a_len+8(FP), AX // len(a) into AX - +8, because first 8 is pointer, second 8 is length, third 8 is cap
SUBQ $8, AX // 8 items or more?
JL remainder
loop:
// a[0]
MOVAPD (SI), X0
MOVAPD (DI), X1
SUBPD X1, X0
MOVAPD X0, (SI)
MOVAPD 16(SI), X2
MOVAPD 16(DI), X3
SUBPD X3, X2
MOVAPD X2, 16(SI)
MOVAPD 32(SI), X4
MOVAPD 32(DI), X5
SUBPD X5, X4
MOVAPD X4, 32(SI)
MOVAPD 48(SI), X6
MOVAPD 48(DI), X7
SUBPD X7, X6
MOVAPD X6, 48(SI)
// update pointers (4 * 2 * 8) - 2*2 elements each time, each element is 8 bytes
ADDQ $64, SI
ADDQ $64, DI
// len(a) is now 8 less
SUBQ $8, AX
JGE loop
remainder:
ADDQ $8, AX
JE done
remainderloop:
// copy into the appropriate registers
MOVSD (SI), X0
MOVSD (DI), X1
SUBSD X1, X0
// save it back
MOVSD X0, (SI)
// update pointer to the top of the data
ADDQ $8, SI
ADDQ $8, DI
DECQ AX
JNE remainderloop
done:
RET
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