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#define BDNZ BC 16,0,
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/*
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* 64/64 division adapted from powerpc compiler writer's handbook
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*
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* (R3:R4) = (R3:R4) / (R5:R6) (64b) = (64b / 64b)
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* quo dvd dvs
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*
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* Remainder is left in R7:R8
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*
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* Code comment notation:
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* msw = most-significant (high-order) word, i.e. bits 0..31
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* lsw = least-significant (low-order) word, i.e. bits 32..63
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* LZ = Leading Zeroes
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* SD = Significant Digits
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*
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* R3:R4 = dvd (input dividend); quo (output quotient)
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* R5:R6 = dvs (input divisor)
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*
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* R7:R8 = tmp; rem (output remainder)
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*/
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TEXT _divu64(SB), $0
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MOVW a+0(FP), R3
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MOVW a+4(FP), R4
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MOVW b+8(FP), R5
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MOVW b+12(FP), R6
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/* count the number of leading 0s in the dividend */
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CMP R3, $0 /* dvd.msw == 0? R3, */
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CNTLZW R3, R11 /* R11 = dvd.msw.LZ */
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CNTLZW R4, R9 /* R9 = dvd.lsw.LZ */
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BNE lab1 /* if(dvd.msw != 0) dvd.LZ = dvd.msw.LZ */
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ADD $32, R9, R11 /* dvd.LZ = dvd.lsw.LZ + 32 */
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lab1:
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/* count the number of leading 0s in the divisor */
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CMP R5, $0 /* dvd.msw == 0? */
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CNTLZW R5, R9 /* R9 = dvs.msw.LZ */
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CNTLZW R6, R10 /* R10 = dvs.lsw.LZ */
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BNE lab2 /* if(dvs.msw != 0) dvs.LZ = dvs.msw.LZ */
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ADD $32, R10, R9 /* dvs.LZ = dvs.lsw.LZ + 32 */
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lab2:
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/* determine shift amounts to minimize the number of iterations */
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CMP R11, R9 /* compare dvd.LZ to dvs.LZ */
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SUBC R11, $64, R10 /* R10 = dvd.SD */
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BGT lab9 /* if(dvs > dvd) quotient = 0 */
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ADD $1, R9 /* ++dvs.LZ (or --dvs.SD) */
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SUBC R9, $64, R9 /* R9 = dvs.SD */
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ADD R9, R11 /* (dvd.LZ + dvs.SD) = left shift of dvd for */
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/* initial dvd */
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SUB R9, R10, R9 /* (dvd.SD - dvs.SD) = right shift of dvd for */
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/* initial tmp */
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MOVW R9, CTR /* number of iterations = dvd.SD - dvs.SD */
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/* R7:R8 = R3:R4 >> R9 */
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CMP R9, $32
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ADD $-32, R9, R7
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BLT lab3 /* if(R9 < 32) jump to lab3 */
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SRW R7, R3, R8 /* tmp.lsw = dvd.msw >> (R9 - 32) */
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MOVW $0, R7 /* tmp.msw = 0 */
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BR lab4
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lab3:
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SRW R9, R4, R8 /* R8 = dvd.lsw >> R9 */
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SUBC R9, $32, R7
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SLW R7, R3, R7 /* R7 = dvd.msw << 32 - R9 */
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OR R7, R8 /* tmp.lsw = R8 | R7 */
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SRW R9, R3, R7 /* tmp.msw = dvd.msw >> R9 */
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lab4:
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/* R3:R4 = R3:R4 << R11 */
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CMP R11,$32
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ADDC $-32, R11, R9
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BLT lab5 /* (R11 < 32)? */
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SLW R9, R4, R3 /* dvd.msw = dvs.lsw << R9 */
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MOVW $0, R4 /* dvd.lsw = 0 */
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BR lab6
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lab5:
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SLW R11, R3 /* R3 = dvd.msw << R11 */
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SUBC R11, $32, R9
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SRW R9, R4, R9 /* R9 = dvd.lsw >> 32 - R11 */
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OR R9, R3 /* dvd.msw = R3 | R9 */
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SLW R11, R4 /* dvd.lsw = dvd.lsw << R11 */
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lab6:
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/* restoring division shift and subtract loop */
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MOVW $-1, R10
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ADDC $0, R7 /* clear carry bit before loop starts */
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lab7:
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/* tmp:dvd is considered one large register */
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/* each portion is shifted left 1 bit by adding it to itself */
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/* adde sums the carry from the previous and creates a new carry */
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ADDE R4,R4 /* shift dvd.lsw left 1 bit */
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ADDE R3,R3 /* shift dvd.msw to left 1 bit */
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ADDE R8,R8 /* shift tmp.lsw to left 1 bit */
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ADDE R7,R7 /* shift tmp.msw to left 1 bit */
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SUBC R6, R8, R11 /* tmp.lsw - dvs.lsw */
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SUBECC R5, R7, R9 /* tmp.msw - dvs.msw */
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BLT lab8 /* if(result < 0) clear carry bit */
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MOVW R11, R8 /* move lsw */
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MOVW R9, R7 /* move msw */
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ADDC $1, R10, R11 /* set carry bit */
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lab8:
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BDNZ lab7
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ADDE R4,R4 /* quo.lsw (lsb = CA) */
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ADDE R3,R3 /* quo.msw (lsb from lsw) */
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lab10:
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MOVW qp+16(FP), R9
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MOVW rp+20(FP), R10
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CMP R9, $0
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BEQ lab11
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MOVW R3, 0(R9)
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MOVW R4, 4(R9)
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lab11:
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CMP R10, $0
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BEQ lab12
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MOVW R7, 0(R10)
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MOVW R8, 4(R10)
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lab12:
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RETURN
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lab9:
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/* Quotient is 0 (dvs > dvd) */
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MOVW R4, R8 /* rmd.lsw = dvd.lsw */
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MOVW R3, R7 /* rmd.msw = dvd.msw */
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MOVW $0, R4 /* dvd.lsw = 0 */
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MOVW $0, R3 /* dvd.msw = 0 */
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BR lab10
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