csum8.c

   1 /*
   2  * Copyright 2010 Google Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  *
  16  * compute rom checksum byte
  17  */
  18
  19 #include <stdio.h>
  20 #include <unistd.h>
  21 #include <stdlib.h>
  22 #include <fcntl.h>
  23 #include <sys/types.h>
  24
  25 #define MAX_SIZE 65536
  26 unsigned char buf[MAX_SIZE];
  27
  28 int main(int argc, char **argv)
  29 {
  30   ssize_t fsize;
  31   int i, sum, fd;
  32   unsigned char csum;
  33
  34   if (argc < 2) {
  35     fprintf(stderr, "usage: %s filename\n", argv[0]);
  36     exit(1);
  37   }
  38   if ((fd = open(argv[1], O_RDWR)) < 0) {
  39     perror(argv[1]);
  40     exit(1);
  41   }
  42   if ((fsize = read(fd, buf, MAX_SIZE)) < 0) {
  43     perror(argv[1]);
  44     exit(1);
  45   }
  46   if (fsize >= MAX_SIZE && read(fd, &buf[MAX_SIZE - 1], 1) > 0) {
  47     fprintf(stderr, "FAIL: %s is larger than %d bytes\n", argv[1], MAX_SIZE);
  48     exit(1);
  49   }
  50   i = fsize - 2048 * (fsize / 2048);
  51   if (i != 2047) {
  52     fprintf(stderr, "FAIL: %s is %zd bytes, need 2K pad-1\n", argv[1], fsize);
  53     exit(1);
  54   }
  55   for (i = sum = 0; i < fsize; i++) {
  56     sum += buf[i];
  57   }
  58   sum &= 0xff;
  59   csum = -sum & 0xff;
  60   write(fd, &csum, 1);
  61   close(fd);
  62   fprintf(stderr, "%s: sum = 0x%02x, wrote byte 0x%02x\n", argv[1], sum, csum);
  63   return 0;
  64 }