83822d6324
This is likely a sub-optimal interface, but I'm trying not to agonize. The whole point of Mu is to permit radical changes at any point in time.
250 lines
11 KiB
Plaintext
250 lines
11 KiB
Plaintext
# read-byte: one higher-level abstraction atop 'read'.
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#
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# There are many situations where 'read' is a lot to manage, and we need
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# to abstract some details away. One of them is when we want to read a file
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# character by character. In this situation we follow C's FILE data structure,
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# which manages the underlying file descriptor together with the buffer it
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# reads into. We call our version 'buffered-file'. Should be useful with other
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# primitives as well, in later layers.
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== data
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# The buffered file for standard input. Also illustrates the layout for
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# buffered-file.
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Stdin:
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# file descriptor or (address stream)
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00 00 00 00 # 0 = standard input
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# current write index
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00 00 00 00
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# current read index
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00 00 00 00
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# length (8)
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08 00 00 00
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# data
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00 00 00 00 00 00 00 00 # 8 bytes
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# TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But
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# I don't want to type 1024 bytes here.
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== code
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# instruction effective address register displacement immediate
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# . op subop mod rm32 base index scale r32
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# . 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
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# main:
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e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.
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#? e8/call test-read-byte-multiple/disp32
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# syscall(exit, Num-test-failures)
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8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX
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b8/copy-to-EAX 1/imm32
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cd/syscall 0x80/imm8
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# return next byte value in EAX, with top 3 bytes cleared.
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# On EOF, return 0xffffffff.
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read-byte: # f : (address buffered-file) -> byte-or-eof/EAX
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# . prolog
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55/push-EBP
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89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
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# . save registers
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51/push-ECX
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56/push-ESI
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# ESI = f
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8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 6/r32/ESI 8/disp8 . # copy *(EBP+8) to ESI
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# ECX = f->read
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8b/copy 1/mod/*+disp8 6/rm32/ESI . . . 1/r32/ECX 8/disp8 . # copy *(ESI+8) to ECX
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# if (f->read >= f->write) populate stream from file
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3b/compare 1/mod/*+disp8 6/rm32/ESI . . . 1/r32/ECX 4/disp8 . # compare ECX with *(ESI+4)
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7c/jump-if-lesser $read-byte:from-stream/disp8
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# . clear-stream(stream = f+4)
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# . . push args
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8d/copy-address 1/mod/*+disp8 6/rm32/ESI . . . 0/r32/EAX 4/disp8 . # copy ESI+4 to EAX
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50/push-EAX
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . EAX = read(f->fd, stream = f+4)
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# . . push args
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50/push-EAX
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ff 6/subop/push 0/mod/indirect 6/rm32/ESI . . . . . . # push *ESI
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# . . call
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e8/call read/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# if EAX = 0 return 0xffffffff
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81 7/subop/compare 3/mod/direct 0/rm32/EAX . . . . . 0/imm32 # compare EAX
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75/jump-if-not-equal $read-byte:from-stream/disp8
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b8/copy-to-EAX 0xffffffff/imm32
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eb/jump $read-byte:end/disp8
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$read-byte:from-stream:
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# read byte from stream
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# AL = f->data[f->read]
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31/xor 3/mod/direct 0/rm32/EAX . . . 0/r32/EAX . . # clear EAX
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8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/ESI 1/index/ECX . 0/r32/AL 0x10/disp8 . # copy *(ESI+ECX+16) to AL
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# ++f->read
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ff 0/subop/increment 1/mod/*+disp8 6/rm32/ESI . . . . 8/disp8 . # increment *(ESI+8)
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$read-byte:end:
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# . restore registers
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5e/pop-to-ESI
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59/pop-to-ECX
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# . epilog
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89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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5d/pop-to-EBP
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c3/return
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# - tests
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test-read-byte-single:
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# - check that read-byte returns first byte of 'file'
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# setup
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# . clear-stream(_test-stream)
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# . . push args
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68/push _test-stream/imm32
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . clear-stream(_test-buffered-file+4)
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# . . push args
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b8/copy-to-EAX _test-buffered-file/imm32
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05/add-to-EAX 4/imm32
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50/push-EAX
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . write(_test-stream, "Ab")
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# . . push args
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68/push "Ab"/imm32
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68/push _test-stream/imm32
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# . . call
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e8/call write/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# read-byte(_test-buffered-file)
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# . . push args
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68/push _test-buffered-file/imm32
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# . . call
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e8/call read-byte/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# check-ints-equal(EAX, 'A', msg)
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# . . push args
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68/push "F - test-read-byte-single"/imm32
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68/push 0x41/imm32
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50/push-EAX
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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# . end
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c3/return
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test-read-byte-multiple:
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# - call read-byte twice, check that second call returns second byte
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# setup
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# . clear-stream(_test-stream)
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# . . push args
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68/push _test-stream/imm32
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . clear-stream(_test-buffered-file+4)
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# . . push args
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b8/copy-to-EAX _test-buffered-file/imm32
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05/add-to-EAX 4/imm32
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50/push-EAX
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . write(_test-stream, "Ab")
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# . . push args
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68/push "Ab"/imm32
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68/push _test-stream/imm32
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# . . call
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e8/call write/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP
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# read-byte(_test-buffered-file)
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# . . push args
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68/push _test-buffered-file/imm32
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# . . call
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e8/call read-byte/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# read-byte(_test-buffered-file)
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# . . push args
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68/push _test-buffered-file/imm32
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# . . call
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e8/call read-byte/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# check-ints-equal(EAX, 'b', msg)
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# . . push args
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68/push "F - test-read-byte-multiple"/imm32
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68/push 0x62/imm32
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50/push-EAX
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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# . end
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c3/return
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test-read-byte-end-of-file:
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# - call read-byte on an empty 'file', check that it returns -1
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# setup
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# . clear-stream(_test-stream)
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# . . push args
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68/push _test-stream/imm32
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# . clear-stream(_test-buffered-file+4)
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# . . push args
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b8/copy-to-EAX _test-buffered-file/imm32
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05/add-to-EAX 4/imm32
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50/push-EAX
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# . . call
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e8/call clear-stream/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# read-byte(_test-buffered-file)
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# . . push args
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68/push _test-buffered-file/imm32
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# . . call
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e8/call read-byte/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP
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# check-ints-equal(EAX, -1, msg)
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# . . push args
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68/push "F - test-read-byte-end-of-file"/imm32
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68/push -1/imm32
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50/push-EAX
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# . . call
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e8/call check-ints-equal/disp32
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# . . discard args
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81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP
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# . end
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c3/return
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== data
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_test-buffered-file:
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# file descriptor or (address stream)
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_test-stream/imm32
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# current write index
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00 00 00 00
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# current read index
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00 00 00 00
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# length (8)
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08 00 00 00
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# data
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00 00 00 00 00 00 00 00 # 8 bytes
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# . . vim:nowrap:textwidth=0
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