38 lines
2.4 KiB
Plaintext
38 lines
2.4 KiB
Plaintext
# 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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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->= $append-byte:end/disp8 # TODO: abort
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$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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# . 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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# . . vim:nowrap:textwidth=0
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