example/crc32/crc32.cc

// Copyright 2018 The Wuffs Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// ----------------

/*
crc32 prints the CRC-32 checksum (using the IEEE polynomial) of stdin. It is
similar to the standard /usr/bin/crc32 program, except that this example
program only reads from stdin.

This example program differs from the other example Wuffs programs in that it
is written in C++, not C.

$CXX crc32.cc && ./a.out < ../../README.md; rm -f a.out

for a C++ compiler $CXX, such as clang++ or g++.
*/

#include <errno.h>
#include <inttypes.h>
#include <stdio.h>
#include <unistd.h>

// Wuffs ships as a "single file C library" or "header file library" as per
// https://github.com/nothings/stb/blob/master/docs/stb_howto.txt
//
// To use that single file as a "foo.c"-like implementation, instead of a
// "foo.h"-like header, #define WUFFS_IMPLEMENTATION before #include'ing or
// compiling it.
#define WUFFS_IMPLEMENTATION

// Defining the WUFFS_CONFIG__STATIC_FUNCTIONS macro is optional, but it
// demonstrates making all of Wuffs' functions have static storage. The
// motivation is discussed in the "ALLOW STATIC IMPLEMENTATION" section of
// https://raw.githubusercontent.com/nothings/stb/master/docs/stb_howto.txt
#define WUFFS_CONFIG__STATIC_FUNCTIONS

// If building this program in an environment that doesn't easily accommodate
// relative includes, you can use the script/inline-c-relative-includes.go
// program to generate a stand-alone C++ file.
#include "../../release/c/wuffs-unsupported-snapshot.c"

#ifndef SRC_BUFFER_SIZE
#define SRC_BUFFER_SIZE (32 * 1024)
#endif

uint8_t src_buffer[SRC_BUFFER_SIZE];

int main(int argc, char** argv) {
  wuffs_crc32__ieee_hasher h;
  const char* status = h.initialize(sizeof h, WUFFS_VERSION, 0);
  if (status) {
    fprintf(stderr, "%s\n", status);
    return 1;
  }

  while (true) {
    const int stdin_fd = 0;
    ssize_t n = read(stdin_fd, src_buffer, SRC_BUFFER_SIZE);
    if (n < 0) {
      if (errno != EINTR) {
        fprintf(stderr, "%s\n", strerror(errno));
        return 1;
      }
      continue;
    }

    uint32_t checksum =
        h.update(wuffs_base__make_slice_u8(src_buffer, static_cast<size_t>(n)));

    if (n == 0) {
      printf("%08" PRIx32 "\n", checksum);
      return 0;
    }
  }
}