78 lines
4.2 KiB
Plaintext
78 lines
4.2 KiB
Plaintext
# streams: data structure for operating on arrays in a stateful manner
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#
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# A stream looks like this:
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# write: int # index at which writes go
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# read: int # index that we've read until
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# data: (array byte) # prefixed by size as usual
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#
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# some primitives for operating on streams:
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# - clear-stream (clears everything but the data size)
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# - rewind-stream (resets read pointer)
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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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clear-stream: # 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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51/push-ecx
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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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# var count/ecx: int = f->size
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8b/copy 1/mod/*+disp8 0/rm32/eax . . . 1/r32/ecx 8/disp8 . # copy *(eax+8) to ecx
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# var max/ecx: (addr byte) = &f->data[f->size]
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8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/eax 1/index/ecx . 1/r32/ecx 0xc/disp8 . # copy eax+ecx+12 to ecx
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# f->write = 0
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c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0/imm32 # copy to *eax
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# f->read = 0
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c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
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# - clear all stream data
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# - this isn't strictly necessary, and it can slow things down *a lot*, but better safe than sorry.
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# var curr/eax: (addr byte) = f->data
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81 0/subop/add 3/mod/direct 0/rm32/eax . . . . . 0xc/imm32 # add to eax
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$clear-stream:loop:
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# if (curr >= max) break
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39/compare 3/mod/direct 0/rm32/eax . . . 1/r32/ecx . . # compare eax with ecx
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73/jump-if-addr>= $clear-stream:end/disp8
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# *curr = 0
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c6 0/subop/copy-byte 0/mod/direct 0/rm32/eax . . . . . 0/imm8 # copy byte to *eax
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# ++curr
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40/increment-eax
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eb/jump $clear-stream:loop/disp8
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$clear-stream:end:
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# . restore registers
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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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rewind-stream: # 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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# f->read = 0
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c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
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$rewind-stream: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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# . . vim:nowrap:textwidth=0
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