ref: 7628681f83b663609eace87a50f8fbf68c31f40b
dir: /sys/src/libmp/mips/mpvecsub.s/
#define BDNZ BC 16,0, #define BDNE BC 0,2, /* * mpvecadd(mpdigit *a, int alen, mpdigit *b, int blen, mpdigit *sum) * * sum[0:alen] = a[0:alen-1] - b[0:blen-1] * * prereq: alen >= blen, sum has room for alen+1 digits * * R1 == a (first arg passed in R1) * R3 == carry * R4 == alen * R5 == b * R6 == blen * R7 == sum * R2 == temporary * R8 == temporary * R9 == temporary */ TEXT mpvecsub(SB),$-4 MOVW alen+4(FP), R4 MOVW b+8(FP), R5 MOVW blen+12(FP), R6 MOVW sum+16(FP), R7 SUBU R6, R4 /* calculate counter for second loop (alen > blen) */ MOVW R0, R3 /* if blen == 0, don't need to subtract it */ BEQ R6,_sub1 /* sum[0:blen-1],carry = a[0:blen-1] - b[0:blen-1] */ _subloop1: MOVW 0(R1), R8 ADDU $4, R1 MOVW 0(R5), R9 ADDU $4, R5 SUBU R3, R8, R2 SGTU R2, R8, R3 SUBU R9, R2, R8 SGTU R8, R2, R9 ADDU R9, R3 MOVW R8, 0(R7) ADDU $4, R7 SUBU $1, R6 BNE R6, _subloop1 _sub1: /* if alen == blen, we're done */ BEQ R4, _subend /* sum[blen:alen-1],carry = a[blen:alen-1] + 0 + carry */ _subloop2: MOVW 0(R1), R8 ADDU $4, R1 SUBU R3, R8, R2 SGTU R2, R8, R3 MOVW R2, 0(R7) ADDU $4, R7 SUBU $1, R4 BNE R4, _subloop2 /* sum[alen] = carry */ _subend: RET