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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 0x80000000 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 = 8
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| 24 | DIVISOR = 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 #0x80000000,uldivr | Force error result
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| 34 | move.l #0x80000000,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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