5137
A few minor stylistic things that may ease reading, but not significantly
enough that I care to force others to follow them:
* no end-of-line comments for instructions without /rm32
* arguments either at tab stops or after 2 spaces
* compare 'with' when using in asymmetric tests (greater/lesser),
compare 'and' for symmetric equality checking
* prefix internal labels with function name
This commit is contained in:
Kartik Agaram
parent
2d61d10eca
commit
02b105fee4
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@ -14,24 +14,25 @@
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#? cd/syscall 0x80/imm8
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print-int32-decimal: # out : (address stream), n : int32
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# PSEUDOCODE
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# based on K&R itoa: https://en.wikibooks.org/wiki/C_Programming/stdlib.h/itoa
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# push SENTINAL
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# if n >= 0:
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# goto digit-encode
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# else:
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# n = -n
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# negative = true
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# while true:
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# push n % 10 + '0'
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# n = n / 10
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# break if n == 0
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# if negative:
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# push '-'
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# while true:
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# EAX = pop
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# break if EAX == SENTINAL
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# out->data[out->write++] = EAX
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# pseudocode:
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# push sentinel
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# EAX, negative? = abs(n), sign(n)
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# while true
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# sign-extend EAX into EDX
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# EAX, EDX = EAX/10, EAX%10
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# EDX += '0'
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# push EDX
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# if (EAX == 0) break
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# if negative?
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# push '-'
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# while true
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# pop into EAX
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# if (EAX == sentinel) break
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# out->data[out->write] = AL
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# ++out->write
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# (based on K&R itoa: https://en.wikibooks.org/wiki/C_Programming/stdlib.h/itoa)
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# (this pseudocode contains registers because operations like division
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# require specific registers in x86)
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#
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# . prolog
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55/push-EBP
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@ -42,86 +43,60 @@ print-int32-decimal: # out : (address stream), n : int32
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52/push-EDX
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53/push-EBX
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57/push-EDI
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# negative = false
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bf/copy-to-EDI 0/imm32 # EDI = 0
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# push sentinal for $append-loop
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68/push-sentinel 0/imm32
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# EAX = n
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# push sentinel
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68/push 0/imm32/sentinel
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# EAX, negative?/EDI = abs(n), sign(n)
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bf/copy-to-EDI 0/imm32/false
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8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 0xc/disp8 . # EAX = *(EBP+12)
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# if n >= 0 jump to digit-encode
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3d/compare-EAX-and 0/imm32
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7d/jump-if-greater-eq $digit-encode:prelude/disp8
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# else
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# n = -n
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f7 3/subop/negate 3/mod/direct 0/rm32/EAX # EAX = -EAX
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# negative = true
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bf/copy-to-EDI 1/imm32 # EDI = 1
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$digit-encode:prelude:
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3d/compare-EAX-with 0/imm32
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7d/jump-if-greater-or-equal $print-int32-decimal:read/disp8
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f7 3/subop/negate 3/mod/direct 0/rm32/EAX . . . . . . # negate EAX
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bf/copy-to-EDI 1/imm32/true
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$print-int32-decimal:read:
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# EBX = n
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8b/copy 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # EBX = EAX
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$digit-encode-loop:
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$print-int32-decimal:read-loop:
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# EAX = EBX(n)
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89/copy 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # EAX = EBX
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b9/copy-to-ECX 0xa/imm32
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b9/copy-to-ECX 0xa/imm32
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# EAX, EDX = EAX / 10, EAX % 10
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99/sign-extend-EAX-into-EDX
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# EDX:EAX(n) / ECX(10)
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# EDX, EAX = n % 10, n / 10
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f7 7/subop/idiv 3/mod/direct 1/rm32/ECX . . . . . . # divide EDX:EAX by ECX, storing quotient in EAX and remainder in EDX
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81 0/subop/add 3/mod/direct 2/rm32/EDX . . . . . 0x30/imm32 # EDX += '0' (0x30)
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# push n % 10 + '0'
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# EDX += '0'
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81 0/subop/add 3/mod/direct 2/rm32/EDX . . . . . 0x30/imm32 # add to EDX
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# push EDX
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52/push-EDX
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# EBX = n / 10
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89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # EBX = EAX
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# loop if n / 10 > 0
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# if (EAX == 0) break
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3d/compare-EAX-and 0/imm32
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7f/jump-if-greater $digit-encode-loop/disp8
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# else:
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7f/jump-if-greater $print-int32-decimal:read-loop/disp8
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$print-int32-decimal:read-break:
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# if (negative?) push('-')
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8b/copy 3/mod/direct 7/rm32/EDI . . . 0/r32/EAX . . # EAX = EDX
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# . if !negative: goto append-loop
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3d/compare-EAX-and 0/imm32
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74/jump-if-equal $append-loop:prelude/disp8
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# . else
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68/push-negative 0x2d/imm32 # push '-'
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$append-loop:prelude:
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# EBX = &out
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3d/compare-EAX-and 0/imm32
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74/jump-if-equal $print-int32-decimal:write/disp8
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68/push 0x2d/imm32/-
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$print-int32-decimal:write:
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# EBX = out
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8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 3/r32/EBX 8/disp8 . # copy *(EBP+8) to EBX
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$append-loop:
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# EAX = next_character
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$print-int32-decimal:write-loop:
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# pop into EAX
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58/pop-to-EAX
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3d/compare-EAX . . . . . . . 0/imm32 # EAX == 0
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74/jump-if-equal $append-loop:break/disp8
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# ECX = out->write
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# if (EAX == sentinel) break
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3d/compare-EAX-and 0/imm32/sentinel
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74/jump-if-equal $print-int32-decimal:end/disp8
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# out->data[out->write] = AL
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# . ECX = out->write
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8b/copy 0/mod/indirect 3/rm32/EBX . . . 1/r32/ECX . . # ECX = *EBX
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# out->data[out->write] = next_character
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# . ECX = &out->data[out->write]
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8d/copy-address 1/mod/*+disp8 4/rm32/sib 3/base/EBX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EBX+ECX+12 to ECX
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# . out->data[out->write] = EAX
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89/copy 0/mod/indirect 1/rm32/ECX . . . 0/r32/ECX . . # *ECX = EAX
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# out->write++
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ff 0/subop/increment 0/mod/indirect 3/rm32/EBX . . . . . . # (*EBX)++
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eb/jump $append-loop/disp8
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$append-loop:break:
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ff 0/subop/increment 0/mod/indirect 3/rm32/EBX . . . . . . # increment *EBX
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eb/jump $print-int32-decimal:write-loop/disp8
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$print-int32-decimal:end:
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# . reclaim locals
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# . restore registers
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57/pop-to-EDI
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5b/pop-to-EBX
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