# read-byte-buffered: one higher-level abstraction atop 'read'.
#
# There are many situations where 'read' is a lot to manage, and we need
# to abstract some details away. One of them is when we want to read a file
# character by character. In this situation we follow C's FILE data structure,
# which manages the underlying file descriptor together with the buffer it
# reads into. We call our version 'buffered-file'. Should be useful with other
# primitives as well, in later layers.
== data
# The buffered file for standard input. Also illustrates the layout for
# buffered-file.
Stdin:
# file descriptor or (address stream)
0/imm32 # standard input
# current write index
0/imm32
# current read index
0/imm32
# length
8/imm32
# data
00 00 00 00 00 00 00 00 # 8 bytes
# TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But
# I don't want to type in 1024 bytes here.
== 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
# return next byte value in eax, with top 3 bytes cleared.
# On reaching end of file, return 0xffffffff (Eof).
read-byte-buffered: # f : (address buffered-file) -> byte-or-Eof/eax
# . prolog
55/push-ebp
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
# . save registers
51/push-ecx
56/push-esi
# esi = f
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi
# ecx = f->read
8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 8/disp8 . # copy *(esi+8) to ecx
# if (f->read >= f->write) populate stream from file
3b/compare 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # compare ecx with *(esi+4)
7c/jump-if-lesser $read-byte-buffered:from-stream/disp8
# . clear-stream(stream = f+4)
# . . push args
8d/copy-address 1/mod/*+disp8 6/rm32/esi . . . 0/r32/eax 4/disp8 . # copy esi+4 to eax
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . f->read must now be 0; update its cache at ecx
31/xor 3/mod/direct 1/rm32/ecx . . . 1/r32/ecx . . # clear ecx
# . eax = read(f->fd, stream = f+4)
# . . push args
50/push-eax
ff 6/subop/push 0/mod/indirect 6/rm32/esi . . . . . . # push *esi
# . . call
e8/call read/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# if (eax == 0) return 0xffffffff
3d/compare-eax-and 0/imm32
75/jump-if-not-equal $read-byte-buffered:from-stream/disp8
b8/copy-to-eax 0xffffffff/imm32/Eof
eb/jump $read-byte-buffered:end/disp8
$read-byte-buffered:from-stream:
# read byte from stream
# AL = f->data[f->read]
31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax
8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/esi 1/index/ecx . 0/r32/AL 0x10/disp8 . # copy byte at *(esi+ecx+16) to AL
# ++f->read
ff 0/subop/increment 1/mod/*+disp8 6/rm32/esi . . . . 8/disp8 . # increment *(esi+8)
$read-byte-buffered:end:
# . restore registers
5e/pop-to-esi
59/pop-to-ecx
# . epilog
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
5d/pop-to-ebp
c3/return
# - tests
test-read-byte-buffered-single:
# - check that read-byte-buffered returns first byte of 'file'
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . clear-stream(_test-buffered-file+4)
# . . push args
b8/copy-to-eax _test-buffered-file/imm32
05/add-to-eax 4/imm32
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . write(_test-stream, "Ab")
# . . push args
68/push "Ab"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'A', msg)
# . . push args
68/push "F - test-read-byte-buffered-single"/imm32
68/push 0x41/imm32
50/push-eax
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# . end
c3/return
test-read-byte-buffered-multiple:
# - call read-byte-buffered twice, check that second call returns second byte
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . clear-stream(_test-buffered-file+4)
# . . push args
b8/copy-to-eax _test-buffered-file/imm32
05/add-to-eax 4/imm32
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . write(_test-stream, "Ab")
# . . push args
68/push "Ab"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'b', msg)
# . . push args
68/push "F - test-read-byte-buffered-multiple"/imm32
68/push 0x62/imm32
50/push-eax
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# . end
c3/return
test-read-byte-buffered-end-of-file:
# - call read-byte-buffered on an empty 'file', check that it returns Eof
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . clear-stream(_test-buffered-file+4)
# . . push args
b8/copy-to-eax _test-buffered-file/imm32
05/add-to-eax 4/imm32
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 0xffffffff, msg)
# . . push args
68/push "F - test-read-byte-buffered-end-of-file"/imm32
68/push 0xffffffff/imm32/Eof
50/push-eax
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# . end
c3/return
test-read-byte-buffered-refills-buffer:
# - consume buffered-file's buffer, check that next read-byte-buffered still works
# setup
# . clear-stream(_test-stream)
# . . push args
68/push _test-stream/imm32
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . clear-stream(_test-buffered-file+4)
# . . push args
b8/copy-to-eax _test-buffered-file/imm32
05/add-to-eax 4/imm32
50/push-eax
# . . call
e8/call clear-stream/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# . write(_test-stream, "Abcdefgh")
# . . push args
68/push "Abcdefgh"/imm32
68/push _test-stream/imm32
# . . call
e8/call write/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp
# pretend buffer is full
# . _test-buffered-file->read = 6 # >= _test-buffered-file->length
b8/copy-to-eax _test-buffered-file/imm32
c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 8/disp8 6/imm32 # copy to *(eax+8)
# read-byte-buffered(_test-buffered-file)
# . . push args
68/push _test-buffered-file/imm32
# . . call
e8/call read-byte-buffered/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp
# check-ints-equal(eax, 'A', msg)
# . . push args
68/push "F - test-read-byte-buffered-refills-buffer"/imm32
68/push 0x41/imm32
50/push-eax
# . . call
e8/call check-ints-equal/disp32
# . . discard args
81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp
# . end
c3/return
== data
# a test buffered file for _test-stream
_test-buffered-file:
# file descriptor or (address stream)
_test-stream/imm32
# current write index
0/imm32
# current read index
0/imm32
# length
6/imm32
# data
00 00 00 00 00 00 # 6 bytes
_test-input-stream:
# current write index
0/imm32
# current read index
0/imm32
# length
0x100/imm32 # 256 bytes
# data (16 lines x 16 bytes/line)
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
# a test buffered file for _test-input-stream
_test-input-buffered-file:
# file descriptor or (address stream)
_test-input-stream/imm32
# current write index
0/imm32
# current read index
0/imm32
# length
6/imm32
# data
00 00 00 00 00 00 # 6 bytes
# . . vim:nowrap:textwidth=0