# 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: a pointer to the backing store, followed by a 'buffer' stream Stdin: # buffered-file # file descriptor or (addr stream byte) 0/imm32 # standard input $Stdin->buffer: # inlined fields for a stream # 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: (addr buffered-file) -> byte-or-Eof/eax # . prologue 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-< $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 es

discard """
  exitcode: 0
  targets: "c cpp js"
  output: '''19316
'''
"""

from sugar import `->`, `=>`
from math import `^`, sum
from sequtils import filter, map, toSeq

proc f: int =
  toSeq(10..<10_000).filter(a => a == ($a).map(d => (d.ord-'0'.ord).int^4).sum).sum

var a = f()

echo a

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: # buffered-file # file descriptor or (addr stream byte) _test-stream/imm32 $_test-buffered-file->buffer: # 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: # (stream byte) # 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: # buffered-file # file descriptor or (addr stream byte) _test-input-stream/imm32 $_test-input-buffered-file->buffer: # 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