46 lines
855 B
ArmAsm
46 lines
855 B
ArmAsm
/*
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* mpvecdigmulsub(mpdigit *b, int n, mpdigit m, mpdigit *p)
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*
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* p -= b*m
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*
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* each step look like:
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* hi,lo = m*b[i]
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* lo += oldhi + carry
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* hi += carry
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* p[i] += lo
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* oldhi = hi
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*
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* the registers are:
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* hi = DX - constrained by hardware
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* lo = AX - constrained by hardware
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* b = SI - can't be BP
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* p = DI - can't be BP
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* i = BP
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* n = CX - constrained by LOOP instr
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* m = BX
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* oldhi = R8
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*
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*/
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TEXT mpvecdigmulsub(SB),$0
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MOVQ RARG,SI
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MOVL n+8(FP),CX
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MOVL m+16(FP),BX
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MOVQ p+24(FP),DI
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XORL BP,BP
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MOVL BP,R8
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_mulsubloop:
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MOVL (SI)(BP*4),AX /* lo = b[i] */
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MULL BX /* hi, lo = b[i] * m */
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ADDL R8,AX /* lo += oldhi */
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ADCL $0, DX /* hi += carry */
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SUBL AX,(DI)(BP*4)
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ADCL $0, DX /* hi += carry */
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MOVL DX,R8
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INCL BP
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LOOP _mulsubloop
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MOVL CX, AX
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SUBL R8,(DI)(BP*4)
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SBBQ CX, AX
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ORQ $1, AX
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RET
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