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exercise: reimplement writing a string to a stream #22

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exercise: reimplement writing a string to a stream #22

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exercise: reimplement writing a string to a stream
akkartik Apr 26, 2019
faec7a5
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charles-l Apr 27, 2019
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51 changes: 33 additions & 18 deletions subx/057write.subx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,33 +42,48 @@ $write:fake:
50/push-EAX
51/push-ECX
52/push-EDX
53/push-EBX
# ECX = f
8b/copy 1/mod/*+disp8 5/rm32/EBP . . 1/r32/ECX 8/disp8 . # copy *(EBP+8) to ECX

# EAX = s
8b/copy 1/mod/*+disp8 5/rm32/EBP . . 0/r32/EAX 0xc/disp8 . # copy *(EBP+12) to EAX

# push s (arg 3)
50/push-EAX

# EDX = f
8b/copy 1/mod/*+disp8 5/rm32/EBP . . 2/r32/EDX 8/disp8 . # copy *(EBP+8) to EDX

# ECX = f->length
8b/copy 1/mod/*+disp8 2/rm32/EDX . . 1/r32/ECX 8/disp8 . # copy *(EDX+8) to ECX

# ECX = &f->data[f->length]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 2/base/EDX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EDX+ECX+12 to ECX

# push &f->data[f->length] (arg 2)
51/push-ECX

# EDX = f->write
8b/copy 0/mod/indirect 1/rm32/ECX . . . 2/r32/EDX . . # copy *ECX to EDX
# EBX = f->length
8b/copy 1/mod/*+disp8 1/rm32/ECX . . . 3/r32/EBX 8/disp8 . # copy *(ECX+8) to EBX
8b/copy 0/mod/indirect 2/rm32/EDX . . 1/r32/EDX . . # copy *(EDX) to ECX

# ECX = &f->data[f->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 2/base/EDX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EDX+ECX+12 to ECX

# push &f->data[f->write] (arg 1)
51/push-ECX

# EAX = _append-3(&f->data[f->write], &f->data[f->length], s)
# . . push s
ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12)
# . . push &f->data[f->length]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 3/index/EBX . 3/r32/EBX 0xc/disp8 . # copy ECX+EBX+12 to EBX
53/push-EBX
# . . push &f->data[f->write]
8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 2/index/EDX . 3/r32/EBX 0xc/disp8 . # copy ECX+EDX+12 to EBX
53/push-EBX
# . . call
e8/call _append-3/disp32
e8/call _append-3/disp32

# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP

# f->write += EAX
01/add 0/mod/indirect 1/rm32/ECX . . . 0/r32/EAX . . # add EAX to *ECX
01/add 0/mod/indirect 2/rm32/EDX . . . 0/r32/EAX . . # add EAX to *EDX

# . restore registers
5b/pop-to-EBX
5a/pop-to-EDX
59/pop-to-ECX
58/pop-to-EAX

$write:end:
# . epilog
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
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