Mu - 112read-byte.subx

1 # Read a single byte from a stream. 2 # 3 # We need to do this in machine code because streams need to be opaque types, 4 # and we don't yet support opaque types in Mu. 5 6 == code 7 # instruction effective address register displacement immediate 8 # . op subop mod rm32 base index scale r32 9 # . 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 10 11 # Return next byte value in eax, with top 3 bytes cleared. 12 # Abort on reaching end of stream. 13 read-byte: # s: (addr stream byte) -> result/eax: byte 14 # . prologue 15 55/push-ebp 16 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 17 # . save registers 18 51/push-ecx 19 56/push-esi 20 # esi = s 21 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi 22 # ecx = s->read 23 8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # copy *(esi+4) to ecx 24 # if (f->read >= f->write) abort 25 3b/compare 0/mod/indirect 6/rm32/esi . . . 1/r32/ecx . . # compare ecx with *esi 26 0f 8d/jump-if->= $read-byte:abort/disp32 27 # result = f->data[f->read] 28 31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax .

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