| 1 | * ------------------------------------------------------------------------------
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| 2 | * uldiv.s -- unsigned long division, with remainder
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| 3 | * Version 2 -- 1987-06-08 -- D.N. Lynx Crowe
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| 4 | * Lifted from the Alcyon C library by disassembly so I could fix a bug -
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| 5 | * _uldivr must be in the bss segment so the code will work in PROM.
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| 6 | *
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| 7 | * long
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| 8 | * uldiv(dividnd, divisor)
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| 9 | * long dividnd, divisor;
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| 10 | *
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| 11 | * extern long uldivr;
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| 12 | *
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| 13 | * Divides 'dividnd' by 'divisor', treating both as unsigned
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| 14 | * long integers. Returns the quotient and leaves the
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| 15 | * remainder in 'uldivr'. Produces a divide check on division
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| 16 | * by zero, with $80000000 returned for both quotient and
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| 17 | * remainder.
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| 18 | * ------------------------------------------------------------------------------
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| 19 | .text
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| 20 | *
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| 21 | .xdef _uldiv,_uldivr
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| 22 | *
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| 23 | DIVIDEND .equ 8
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| 24 | DIVISOR .equ 12
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| 25 | *
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| 26 | _uldiv: link a6,#0 * Link stack frames
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| 27 | movem.l d3-d7,-(a7) * Save registers
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| 28 | move.l DIVIDEND(a6),d7 * d7 = DIVIDEND
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| 29 | move.l DIVISOR(a6),d6 * d6 = DIVISOR
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| 30 | tst.l d6 * Divide by zero ?
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| 31 | bne notdzero * Jump if not
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| 32 | *
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| 33 | move.l #$80000000,_uldivr * Force error result
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| 34 | move.l #$80000000,d0 * ... by dividing
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| 35 | divu #0,d0 * ... by zero
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| 36 | bra ulexit * ... then exit
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| 37 | *
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| 38 | notdzero: cmp.l d7,d6 * Divide underflow ?
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| 39 | bls notunflo * Jump if not
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| 40 | *
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| 41 | move.l d7,_uldivr * Remainder = dividend
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| 42 | clr.l d0 * Quotient = 0
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| 43 | bra ulexit * Exit
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| 44 | *
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| 45 | notunflo: cmp.l d6,d7 * Is dividend = divisor ?
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| 46 | bne startdiv * Go start dividing if not
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| 47 | *
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| 48 | moveq.l #1,d5 * Quotient = 1
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| 49 | clr.l d7 * Remainder = 0
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| 50 | bra setreslt * Go set result
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| 51 | *
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| 52 | .page
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| 53 | *
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| 54 | startdiv: moveq.l #1,d4 * Set result bit in d4
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| 55 | *
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| 56 | divloop1: cmp.l d6,d7 * Divisor aligned OK ?
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| 57 | bcs divloop2 * Jump if so
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| 58 | *
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| 59 | move.l d6,d0 * Can we align things better ?
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| 60 | asl.l #1,d0 * ...
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| 61 | cmp.l d0,d6 * ...
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| 62 | bhi divloop2 * Jump if not
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| 63 | *
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| 64 | asl.l #1,d6 * Shift the divisor
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| 65 | asl.l #1,d4 * Shift the result bit
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| 66 | bra divloop1 * Loop for next bit
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| 67 | *
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| 68 | divloop2: clr.l d5 * Clear quotient
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| 69 | *
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| 70 | divloop3: tst.l d4 * More bits to do ?
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| 71 | beq setreslt * Go set result if not
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| 72 | *
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| 73 | cmp.l d6,d7 * Can we subtract ?
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| 74 | bcs divloop4 * Jump if not
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| 75 | *
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| 76 | or.l d4,d5 * Set a bit in the quotient
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| 77 | sub.l d6,d7 * Subtract divisor from dividend
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| 78 | *
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| 79 | divloop4: lsr.l #1,d4 * Shift the result bit
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| 80 | lsr.l #1,d6 * Shift the divisor
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| 81 | bra divloop3 * Loop for next bit
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| 82 | *
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| 83 | setreslt: move.l d7,_uldivr * Store remainder
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| 84 | move.l d5,d0 * Put quotient in d0
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| 85 | *
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| 86 | ulexit: tst.l (a7)+ * Discard top of stack
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| 87 | movem.l (a7)+,d4-d7 * Restore registers
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| 88 | unlk a6 * Unlink stack frames
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| 89 | rts * Return to caller
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| 90 | *
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| 91 | .bss
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| 92 | .even
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| 93 | *
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| 94 | _uldivr: ds.l 1
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| 95 | *
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| 96 | .end
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