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# streams: data structure for operating on arrays in a stateful manner
#
# A stream looks like this:
# write: int # index at which writes go
# read: int # index that we've read until
# data: (array byte) # prefixed by size as usual
#
# some primitives for operating on streams:
# - clear-stream (clears everything but the data size)
# - rewind-stream (resets read pointer)
#
# We need to do this in machine code because streams need to be opaque types,
# and we don't yet support opaque types in Mu.
== code
# instruction effective address register displacement immediate
# . op subop mod rm32 base index scale r32
# . 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
clear-stream: # f: (addr stream byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
51/push-ecx
# eax = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
# var count/ecx: int = f->size
8b/copy 1/mod/*+disp8 0/rm32/eax . . . 1/r32/ecx 8/disp8 . # copy *(eax+8) to ecx
# var max/ecx: (addr byte) = &f->data[f->size]
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
# f->write = 0
c7 0/subop/copy 0/mod/direct 0/rm32/eax . . . . . 0/imm32 # copy to *eax
# f->read = 0
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
# - clear all stream data
# - this isn't strictly necessary, and it can slow things down *a lot*, but better safe than sorry.
# var curr/eax: (addr byte) = f->data
81 0/subop/add 3/mod/direct 0/rm32/eax . . . . . 0xc/imm32 # add to eax
$clear-stream:loop:
# if (curr >= max) break
39/compare 3/mod/direct 0/rm32/eax . . . 1/r32/ecx . . # compare eax with ecx
73/jump-if-addr>= $clear-stream:end/disp8
# *curr = 0
c6 0/subop/copy-byte 0/mod/direct 0/rm32/eax . . . . . 0/imm8 # copy byte to *eax
# ++curr
40/increment-eax
eb/jump $clear-stream:loop/disp8
$clear-stream:end:
# . restore registers
59/pop-to-ecx
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
rewind-stream: # f: (addr stream byte)
# . prologue
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
50/push-eax
# eax = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . 0/r32/eax 8/disp8 . # copy *(ebp+8) to eax
# f->read = 0
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 4/disp8 0/imm32 # copy to *(eax+4)
$rewind-stream:end:
# . restore registers
58/pop-to-eax
# . epilogue
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
# . . vim:nowrap:textwidth=0
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