# 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