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104 lines
5.1 KiB
104 lines
5.1 KiB
# Write a single byte to a stream. |
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# |
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# We need to do this in machine code because streams need to be opaque types, |
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# and we don't yet support opaque types in Mu. |
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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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# Write lower byte of 'n' to 'f'. |
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append-byte: # f: (addr stream byte), n: int |
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# . prologue |
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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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50/push-eax |
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51/push-ecx |
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57/push-edi |
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# edi = f |
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 7/r32/edi 8/disp8 . # copy *(ebp+8) to edi |
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# ecx = f->write |
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8b/copy 0/mod/indirect 7/rm32/edi . . . 1/r32/ecx . . # copy *edi to ecx |
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# if (f->write >= f->size) abort |
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3b/compare 1/mod/*+disp8 7/rm32/edi . . . 1/r32/ecx 8/disp8 . # compare ecx with *(edi+8) |
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7d/jump-if->= $append-byte:abort/disp8 |
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$append-byte:to-stream: |
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# write to stream |
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# f->data[f->write] = LSB(n) |
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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 5/rm32/ebp . . . 0/r32/AL 0xc/disp8 . # copy byte at *(ebp+12) to AL |
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88/copy-byte 1/mod/*+disp8 4/rm32/sib 7/base/edi 1/index/ecx . 0/r32/AL 0xc/disp8 . # copy AL to *(edi+ecx+12) |
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# ++f->write |
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ff 0/subop/increment 0/mod/indirect 7/rm32/edi . . . . . . # increment *edi |
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$append-byte:end: |
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# . restore registers |
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5f/pop-to-edi |
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59/pop-to-ecx |
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58/pop-to-eax |
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# . epilogue |
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89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp |
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5d/pop-to-ebp |
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c3/return |
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$append-byte:abort: |
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(abort "append-byte: out of space") |
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# never gets here |
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test-append-byte-single: |
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# - check that append-byte writes to 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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# append-byte(_test-stream, 'A') |
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# . . push args |
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68/push 0x41/imm32 |
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68/push _test-stream/imm32 |
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# . . call |
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e8/call append-byte/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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# check-stream-equal(_test-stream, "A", msg) |
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# . . push args |
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68/push "F - test-append-byte-single"/imm32 |
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68/push "A"/imm32 |
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68/push _test-stream/imm32 |
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# . . call |
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e8/call check-stream-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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undo-append-byte: # f: (addr stream byte) |
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# . prologue |
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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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50/push-eax |
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# eax = f |
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8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax |
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# if (f->write <= 0) abort |
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81 7/subop/compare 0/mod/indirect 0/rm32/eax . . . . . 0/imm32 # compare *eax |
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7e/jump-if-<= $undo-append-byte:abort/disp8 |
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# --f->write |
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ff 1/subop/decrement 0/mod/indirect 0/rm32/eax . . . . . . # decrement *eax |
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$undo-append-byte:end: |
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# . restore registers |
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58/pop-to-eax |
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# . epilogue |
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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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$undo-append-byte:abort: |
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(abort "undo-append-byte: empty stream") |
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# never gets here |
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# . . vim:nowrap:textwidth=0
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