80 lines
2.0 KiB
ArmAsm
80 lines
2.0 KiB
ArmAsm
// Scalar ARM64 implementation of ycoCgToBGRANEON.
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// Processes one pixel per iteration (no chroma subsampling, alpha = 0xFF).
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// Go arm64 assembler lacks SSHR (signed vector shift right), SSHL (by register),
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// and SQXTUN (saturating narrow), so we use scalar GP instructions instead.
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// Stack ABI (ABI0):
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// pixels+0(FP) unsafe.Pointer
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// yPlane+8(FP) unsafe.Pointer
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// coPlane+16(FP) unsafe.Pointer
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// cgPlane+24(FP) unsafe.Pointer
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// count+32(FP) int
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// shift+40(FP) int
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#include "textflag.h"
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// func ycoCgToBGRANEON(pixels, yPlane, coPlane, cgPlane unsafe.Pointer, count, shift int)
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TEXT ·ycoCgToBGRANEON(SB),NOSPLIT,$0-48
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MOVD pixels+0(FP), R0 // dst
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MOVD yPlane+8(FP), R1 // Y plane
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MOVD coPlane+16(FP), R2 // Co plane
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MOVD cgPlane+24(FP), R3 // Cg plane
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MOVD count+32(FP), R4 // pixel count
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MOVD shift+40(FP), R5 // shift amount
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CBZ R4, done
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MOVD $0, R12 // const 0
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MOVD $255, R13 // const 255
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loop:
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MOVBU (R1), R6 // y = Y[i]
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MOVBU (R2), R7 // co = Co[i]
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MOVBU (R3), R8 // cg = Cg[i]
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ADD $1, R1
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ADD $1, R2
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ADD $1, R3
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// coVal = int8(co << shift): shift left, then sign-extend low byte.
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LSL R5, R7, R7 // R7 = co << shift (low 8 bits hold result)
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SXTB R7, R7 // R7 = int64(int8(R7))
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// cgVal = int8(cg << shift)
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LSL R5, R8, R8
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SXTB R8, R8
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// B = clamp(y - co - cg)
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SUB R7, R6, R9 // R9 = y - co
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SUB R8, R9, R9 // R9 = y - co - cg
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CMP R12, R9
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CSEL LT, R12, R9, R9
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CMP R13, R9
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CSEL GT, R13, R9, R9
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// G = clamp(y + cg)
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ADD R8, R6, R10 // R10 = y + cg
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CMP R12, R10
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CSEL LT, R12, R10, R10
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CMP R13, R10
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CSEL GT, R13, R10, R10
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// R = clamp(y + co - cg)
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ADD R7, R6, R11 // R11 = y + co
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SUB R8, R11, R11 // R11 = y + co - cg
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CMP R12, R11
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CSEL LT, R12, R11, R11
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CMP R13, R11
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CSEL GT, R13, R11, R11
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// Store BGRA pixel.
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MOVBU R9, 0(R0)
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MOVBU R10, 1(R0)
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MOVBU R11, 2(R0)
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MOVBU R13, 3(R0) // alpha = 255
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ADD $4, R0
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SUBS $1, R4, R4
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BNE loop
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done:
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RET
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