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I've wrestled for a long time with how to support integer division with its hard-coded registers. The answer's always been staring me in the face: just turn it into a function! We already expect function outputs to go to hard-coded registers.
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== code
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integer-divide: # a: int, b: int -> quotient/eax: int, remainder/edx: int
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# . prologue
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55/push-ebp
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89/<- %ebp 4/r32/esp
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# eax = a
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8b/-> *(ebp+8) 0/r32/eax
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# edx = all 0s or all 1s
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99/sign-extend-eax-into-edx
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# quotient, remainder = divide eax by b
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f7 7/subop/divide-eax-edx-by *(ebp+0xc)
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$integer-divide:end:
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# . epilogue
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89/<- %esp 5/r32/ebp
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5d/pop-to-ebp
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c3/return
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2
400.mu
2
400.mu
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@ -185,3 +185,5 @@ sig stream-final s: (addr stream byte) -> _/eax: byte
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#sig copy-bytes src: (addr byte), dest: (addr byte), n: int
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sig copy-array-object src: (addr array _), dest-ah: (addr handle array _)
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sig copy-file src: (addr buffered-file), dest-ah: (addr handle buffered-file), filename: (addr array byte)
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sig integer-divide a: int, b: int -> _/eax: int, _/edx: int
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101
406int32.mu
101
406int32.mu
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@ -1,106 +1,5 @@
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# Some slow but convenient helpers
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# slow, iterative divide instruction
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# preconditions: _nr >= 0, _dr > 0
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fn try-divide _nr: int, _dr: int -> _/eax: int {
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# x = next power-of-2 multiple of _dr after _nr
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var x/ecx: int <- copy 1
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{
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#? print-int32-hex 0, x
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#? print-string 0, "\n"
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var tmp/edx: int <- copy _dr
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tmp <- multiply x
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compare tmp, _nr
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break-if->
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x <- shift-left 1
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loop
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}
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#? print-string 0, "--\n"
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# min, max = x/2, x
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var max/ecx: int <- copy x
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var min/edx: int <- copy max
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min <- shift-right 1
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# narrow down result between min and max
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var i/eax: int <- copy min
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{
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#? print-int32-hex 0, i
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#? print-string 0, "\n"
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var foo/ebx: int <- copy _dr
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foo <- multiply i
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compare foo, _nr
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break-if->
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i <- increment
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loop
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}
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var result/eax: int <- copy i
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result <- decrement
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#? print-string 0, "=> "
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#? print-int32-hex 0, result
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#? print-string 0, "\n"
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return result
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}
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fn test-try-divide-1 {
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var result/eax: int <- try-divide 0, 2
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check-ints-equal result, 0, "F - try-divide-1"
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}
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fn test-try-divide-2 {
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var result/eax: int <- try-divide 1, 2
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check-ints-equal result, 0, "F - try-divide-2"
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}
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fn test-try-divide-3 {
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var result/eax: int <- try-divide 2, 2
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check-ints-equal result, 1, "F - try-divide-3"
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}
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fn test-try-divide-4 {
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var result/eax: int <- try-divide 4, 2
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check-ints-equal result, 2, "F - try-divide-4"
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}
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fn test-try-divide-5 {
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var result/eax: int <- try-divide 6, 2
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check-ints-equal result, 3, "F - try-divide-5"
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}
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fn test-try-divide-6 {
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var result/eax: int <- try-divide 9, 3
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check-ints-equal result, 3, "F - try-divide-6"
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}
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fn test-try-divide-7 {
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var result/eax: int <- try-divide 0xc, 4
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check-ints-equal result, 3, "F - try-divide-7"
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}
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fn test-try-divide-8 {
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var result/eax: int <- try-divide 0x1b, 3 # 27/3
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check-ints-equal result, 9, "F - try-divide-8"
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}
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fn test-try-divide-9 {
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var result/eax: int <- try-divide 0x1c, 3 # 28/3
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check-ints-equal result, 9, "F - try-divide-9"
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}
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# only positive dr for now
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fn try-modulo nr: int, dr: int -> _/eax: int {
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var _positive-nr/eax: int <- abs nr
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var positive-nr/ecx: int <- copy _positive-nr
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var result/eax: int <- try-divide positive-nr, dr
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result <- multiply dr
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result <- subtract positive-nr
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result <- negate
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return result
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}
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fn test-try-modulo-negative-nr {
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var result/eax: int <- try-modulo -0xa, 7
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check-ints-equal result, 3, "F - test-try-modulo-negative-nr"
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}
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# slow, iterative shift-left instruction
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# preconditions: _nr >= 0, _dr > 0
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fn repeated-shift-left nr: int, dr: int -> _/eax: int {
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@ -155,8 +155,10 @@ fn render-screen screen: (addr screen), row: int, col: int, _target-screen: (add
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}
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fn hash-color val: int -> _/eax: int {
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var result/eax: int <- try-modulo val, 7 # assumes that 7 is always the background color
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return result
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var quotient/eax: int <- copy 0
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var remainder/edx: int <- copy 0
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quotient, remainder <- integer-divide val, 7 # assumes that 7 is always the background color
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return remainder
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}
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fn print-screen-cell-of-fake-screen screen: (addr screen), _target: (addr screen), _row: int, _col: int {
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