1 #   instruction                     effective address                                                   register    displacement    immediate
 2 # . op          subop               mod             rm32          base        index         scale       r32
 3 # . 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
 4 
 5 # TODO: read-byte-buffered
 6 
 7 # Return next byte value in eax, with top 3 bytes cleared.
 8 # Abort on reaching end of stream.
 9 read-byte:  # s: (addr stream byte) -> result/eax: byte
10     # . prologue
11     55/push-ebp
12     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
13     # . save registers
14     51/push-ecx
15     56/push-esi
16     # esi = s
17     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           6/r32/esi   8/disp8         .                 # copy *(ebp+8) to esi
18     # ecx = s->read
19     8b/copy                         1/mod/*+disp8   6/rm32/esi    .           .             .           1/r32/ecx   4/disp8         .                 # copy *(esi+4) to ecx
20     # if (f->read >= f->write) abort
21     3b/compare                      0/mod/indirect  6/rm32/esi    .           .             .           1/r32/ecx   .               .                 # compare ecx with *esi
22     0f 8d/jump-if->=  $read-byte:end/disp32  # TODO: abort
23     # result = f->data[f->read]
24     31/xor                          3/mod/direct    0/rm32/eax    .           .             .           0/r32/eax   .               .                 # clear eax
25     8a/copy-byte                    1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx   .           0/r32/AL    0xc/disp8       .                 # copy byte at *(esi+ecx+12) to AL
26     # ++f->read
27     ff          0/subop/increment   1/mod/*+disp8   6/rm32/esi    .           .             .           .           4/disp8         .                 # increment *(esi+4)
28 $read-byte:end:
29     # . restore registers
30     5e/pop-to-esi
31     59/pop-to-ecx
32     # . epilogue
33     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
34     5d/pop-to-ebp
35     c3/return
36 
37 # . . vim:nowrap:textwidth=0