# Helper to print an int32 in decimal.
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
print-int32-decimal: # out : (address stream), n : int32
# works by generating characters from lowest to highest and pushing them
# to the stack, before popping them one by one into the stream
#
# pseudocode:
# push sentinel
# EAX = abs(n)
# while true
# sign-extend EAX into EDX
# EAX, EDX = EAX/10, EAX%10
# EDX += '0'
# push EDX
# if (EAX == 0) break
# if n < 0
# push '-'
# w = out->write
# curr = &out->data[out->write]
# max = &out->data[out->length]
# while true
# pop into EAX
# if (EAX == sentinel) break
# if (curr >= max) abort
# *curr = AL
# ++curr
# ++w
# out->write = w
# (based on K&R itoa: https://en.wikibooks.org/wiki/C_Programming/stdlib.h/itoa)
# (this pseudocode contains registers because operations like division
# require specific registers in x86)
#
# . prolog
55/push-EBP
89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
# . save registers
50/push-EAX
51/push-ECX
52/push-EDX
53/push-EBX
57/push-EDI
# ten/ECX = 10
b9/copy-to-ECX 0xa/imm32
# push sentinel
68/push 0/imm32/sentinel
# EAX = abs(n)
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 0/r32/EAX 0xc/disp8 . # copy *(EBP+12) to EAX
3d/compare-EAX-with 0/imm32
7d/jump-if-greater-or-equal $print-int32-decimal:read-loop/disp8
$print-int32-decimal:negative:
f7 3/subop/negate 3/mod/direct 0/rm32/EAX . . . . . . # negate EAX
$print-int32-decimal:read-loop:
# EAX, EDX = EAX / 10, EAX % 10
99/sign-extend-EAX-into-EDX
f7 7/subop/idiv 3/mod/direct 1/rm32/ECX . . . . . . # divide EDX:EAX by ECX, storing quotient in EAX and remainder in EDX
# EDX += '0'
81 0/subop/add 3/mod/direct 2/rm32/EDX . . . . . 0x30/imm32 # add to EDX
# push EDX
52/push-EDX
# if (EAX == 0) break
3d/compare-EAX-and 0/imm32
7f/jump-if-greater $print-int32-decimal:read-loop/disp8
$print-int32-decimal:read-break:
# if (n < 0) push('-')
81 7/subop/compare 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 0/imm32 # compare *(EBP+12)
7d/jump-if-greater-or-equal $print-int32-decimal:write/disp8
$print-int32-decimal:push-negative:
68/push 0x2d/imm32/-
$print-int32-decimal:write:
# EDI = out
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI
# w/EDX = out->write
8b/copy 0/mod/indirect 7/rm32/EDI . . . 2/r32/EDX . . # copy *EDI to EDX
# curr/ECX = &out->data[out->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 7/base/EDI 2/index/EDX . 1/r32/ECX 0xc/disp8 . # copy EBX+EDX+12 to ECX
# max/EBX = &out->data[out->length]
8b/copy 1/mod/*+disp8 7/rm32/EDI . . . 3/r32/EBX 8/disp8 . # copy *(EDI+8) to EBX
8d/copy-address 1/mod/*+disp8 4/rm32/sib 7/base/EDI 3/index/EBX . 3/r32/EBX 0xc/disp8 . # copy EDI+EBX+12 to EBX
$print-int32-decimal:write-loop:
# pop into EAX
58/pop-to-EAX
# if (EAX == sentinel) break
3d/compare-EAX-and 0/imm32/sentinel
74/jump-if-equal $print-int32-decimal:write-break/disp8
# if (curr >= max) abort
39/compare 3/mod/direct 1/rm32/ECX . . . 3/r32/EBX . . # compare ECX with EBX
73/jump-if-greater-or-equal-unsigned $print-int32-decimal:abort/disp8
$print-int32-decimal:write-char:
# *curr = AL
88/copy-byte 0/mod/indirect 1/rm32/ECX . . . 0/r32/AL . . # copy AL to byte at *ECX
# ++curr
41/increment-ECX
# ++w
42/increment-EDX
eb/jump $print-int32-decimal:write-loop/disp8
$print-int32-decimal:write-break:
# out->write = w
89/copy 0/mod/indirect 7/rm32/EDI . . . 2/r32/EDX . . # copy EDX to *EDI
$print-int32-decimal:end:
# . restore registers
5f/pop-to-EDI
5b/pop-to-EBX
5a/pop-to-EDX
59/pop-to-ECX
58/pop-to-EAX
# . epilog
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
5d/pop-to-EBP
c3/return
$print-int32-decimal:abort:
# . _write(2/stderr, error)
# . . push args
68/push "print-int32-decimal: out of space\n"/imm32
68/push 2/imm32/stderr
# . . call
e8/call _write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
# . syscall(exit, 1)
bb/copy-to-EBX 1/imm32
b8/copy-to-EAX 1/imm32/exit
cd/syscall 0x80/imm8
# never gets here
test-print-int32-decimal:
# - check that a single-digit number converts correctly
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
# print-int32-decimal(_test-stream, 9)
# . . push args
68/push 9/imm32
68/push _test-stream/imm32
# . . call
e8/call print-int32-decimal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
# check-stream-equal(_test-stream, "9", msg)
# . . push args
68/push "F - test-print-int32-decimal"/imm32
68/push "9"/imm32
68/push _test-stream/imm32
# . . call
e8/call check-stream-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
# . end
c3/return
test-print-int32-decimal-zero:
# - check that 0 converts correctly
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
# print-int32-decimal(_test-stream, 0)
# . . push args
68/push 0/imm32
68/push _test-stream/imm32
# . . call
e8/call print-int32-decimal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
# check-stream-equal(_test-stream, "0", msg)
# . . push args
68/push "F - test-print-int32-decimal-zero"/imm32
68/push "0"/imm32
68/push _test-stream/imm32
# . . call
e8/call check-stream-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
# . end
c3/return
test-print-int32-decimal-multiple-digits:
# - check that a multi-digit number converts correctly
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
# print-int32-decimal(_test-stream, 10)
# . . push args
68/push 0xa/imm32
68/push _test-stream/imm32
# . . call
e8/call print-int32-decimal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
# check-stream-equal(_test-stream, "10", msg)
# . . push args
68/push "F - test-print-int32-decimal-multiple-digits"/imm32
68/push "10"/imm32
68/push _test-stream/imm32
# . . call
e8/call check-stream-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
# . end
c3/return
test-print-int32-decimal-negative:
# - check that a negative single-digit number converts correctly
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
# print-int32-decimal(_test-stream, -9)
# . . push args
68/push -9/imm32
68/push _test-stream/imm32
# . . call
e8/call print-int32-decimal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
#? # dump _test-stream {{{
#? # . write(2/stderr, "^")
#? # . . push args
#? 68/push "^"/imm32
#? 68/push 2/imm32/stderr
#? # . . call
#? e8/call write/disp32
#? # . . discard args
#? 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
#? # . write-stream(2/stderr, _test-stream)
#? # . . push args
#? 68/push _test-stream/imm32
#? 68/push 2/imm32/stderr
#? # . . call
#? e8/call write-stream/disp32
#? # . . discard args
#? 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
#? # . write(2/stderr, "$\n")
#? # . . push args
#? 68/push "$\n"/imm32
#? 68/push 2/imm32/stderr
#? # . . call
#? e8/call write/disp32
#? # . . discard args
#? 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
#? # }}}
# check-stream-equal(_test-stream, "-9", msg)
# . . push args
68/push "F - test-print-int32-decimal-negative"/imm32
68/push "-9"/imm32
68/push _test-stream/imm32
# . . call
e8/call check-stream-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
# . end
c3/return
test-print-int32-decimal-negative-multiple-digits:
# - check that a multi-digit number converts correctly
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
# print-int32-decimal(_test-stream, -10)
# . . push args
68/push -0xa/imm32
68/push _test-stream/imm32
# . . call
e8/call print-int32-decimal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
# check-stream-equal(_test-stream, "-10", msg)
# . . push args
68/push "F - test-print-int32-decimal-negative-multiple-digits"/imm32
68/push "-10"/imm32
68/push _test-stream/imm32
# . . call
e8/call check-stream-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
# . end
c3/return
# . . vim:nowrap:textwidth=0