451 lines
13 KiB
C
Executable File
451 lines
13 KiB
C
Executable File
/* compress.c -- Byte Pair Encoding compression */
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/* Copyright 1996 Philip Gage */
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/* This program appeared in the September 1997 issue of
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* C/C++ Users Journal. The original source code may still
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* be found at the web site of the magazine (www.cuj.com).
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*
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* It has been modified by me (Thiadmer Riemersma) to
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* compress only a section of the input file and to store
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* the compressed output along with the input as "C" strings.
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*
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* Compiling instructions:
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* Borland C++ 16-bit (large memory model is required):
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* bcc -ml scpack.c
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*
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* Watcom C/C++ 32-bit:
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* wcl386 scpack.c
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*
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* GNU C (Linux), 32-bit:
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* gcc scpack.c -o scpack
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*/
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#include <assert.h>
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#include <limits.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#if UINT_MAX > 0xFFFFU
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#define MAXSIZE 1024*1024L
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#else
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#define MAXSIZE UINT_MAX /* Input file buffer size */
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#endif
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#define HASHSIZE 8192 /* Hash table size, power of 2 */
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#define THRESHOLD 3 /* Increase for speed, min 3 */
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#define START_TOKEN "#ifdef SCPACK" /* start reading the buffer here */
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#define NAME_TOKEN "#define SCPACK_TABLE"
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#define SEP_TOKEN "#define SCPACK_SEPARATOR"
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#define TERM_TOKEN "#define SCPACK_TERMINATOR"
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#define TEMPFILE "~SCPACK.TMP"
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static char tablename[32+1] = "scpack_table";
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static char separator[16]=",";
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static char terminator[16]="";
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int compress(unsigned char *buffer, unsigned buffersize, unsigned char pairtable[128][2])
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{
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unsigned char *left, *right, *count;
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unsigned char a, b, bestcount;
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unsigned i, j, index, bestindex, code=128;
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/* Dynamically allocate buffers and check for errors */
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left = (unsigned char *)malloc(HASHSIZE);
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right = (unsigned char *)malloc(HASHSIZE);
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count = (unsigned char *)malloc(HASHSIZE);
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if (left==NULL || right==NULL || count==NULL) {
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printf("Error allocating memory\n");
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exit(1);
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}
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/* Check for errors */
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for (i=0; i<buffersize; i++)
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if (buffer[i] > 127) {
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printf("This program works only on text files (7-bit ASCII)\n");
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exit(1);
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}
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memset(pairtable, 0, 128*2*sizeof(char));
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do { /* Replace frequent pairs with bytes 128..255 */
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/* Enter counts of all byte pairs into hash table */
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memset(count,0,HASHSIZE);
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for (i=0; i<buffersize-1; i++) {
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a = buffer[i];
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b = buffer[i+1];
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/* ignore any pair with a '\0' */
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if (a == 0 || b == 0)
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continue;
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index = (a ^ (b << 6)) & (HASHSIZE-1);
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while ((left[index] != a || right[index] != b) &&
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count[index] != 0)
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index = (index + 1) & (HASHSIZE-1);
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left[index] = a;
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right[index] = b;
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if (count[index] < 255)
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count[index] += (unsigned char)1;
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}
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/* Search hash table for most frequent pair */
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bestcount = THRESHOLD - 1;
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for (i=0; i<HASHSIZE; i++) {
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if (count[i] > bestcount) {
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bestcount = count[i];
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bestindex = i;
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}
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}
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/* Compress if enough occurrences of pair */
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if (bestcount >= THRESHOLD) {
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/* Add pair to table using code as index */
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a = pairtable[code-128][0] = left[bestindex];
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b = pairtable[code-128][1] = right[bestindex];
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/* Replace all pair occurrences with unused byte */
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for (i=0, j=0; i<buffersize; i++, j++)
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if (a == buffer[i] && b == buffer[i+1]) {
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buffer[j] = (unsigned char)code;
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++i;
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}
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else
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buffer[j] = buffer[i];
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buffersize = j;
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}
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else
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break;
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} while (++code < 255);
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/* done */
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free(left); free(right); free(count);
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return buffersize; /* return adjusted buffersize */
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}
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static int strmatch(char *str, char *token, int *indent)
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{
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int i = 0;
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/* skip whitespace */
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while (*str==' ' || *str=='\t') {
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str++;
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i++;
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} /* while */
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if (strncmp(str,token,strlen(token))!=0)
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return 0;
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if (indent != NULL)
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*indent = i;
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return 1;
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}
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static void check_if(char *str,int linenr)
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{
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if (strmatch(str,"#if",NULL)) {
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printf("Error: \"#if...\" preprocessor statement should not be in SCPACK section "
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"(line %d)\n", linenr);
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exit(1);
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} /* if */
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}
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static int check_tablename(char *str)
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{
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int i;
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if (strmatch(str,NAME_TOKEN,NULL)) {
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str += strlen(NAME_TOKEN);
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while (*str==' ' || *str=='\t')
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str++;
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for (i=0; i<(sizeof tablename - 1) && *str!='\0' && strchr(" \t\n",*str)==NULL; i++, str++)
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tablename[i] = *str;
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tablename[i] = '\0';
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return 1;
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} /* if */
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return 0;
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}
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static int check_separator(char *str)
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{
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int i;
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if (strmatch(str,SEP_TOKEN,NULL)) {
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str += strlen(SEP_TOKEN);
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while (*str==' ' || *str=='\t')
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str++;
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for (i=0; i<(sizeof separator - 1) && *str!='\0' && strchr(" \t\n",*str)==NULL; i++, str++)
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separator[i] = *str;
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separator[i] = '\0';
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return 1;
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} /* if */
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if (strmatch(str,TERM_TOKEN,NULL)) {
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str += strlen(TERM_TOKEN);
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while (*str==' ' || *str=='\t')
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str++;
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for (i=0; i<(sizeof terminator - 1) && *str!='\0' && strchr(" \t\n",*str)==NULL; i++, str++)
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terminator[i] = *str;
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terminator[i] = '\0';
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return 1;
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} /* if */
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return 0;
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}
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/* readbuffer
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* Reads in the input file and stores all strings in the
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* section between "#ifdef SCPACK" and "#else" in a buffer.
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* Only text that is between double quotes is added to the
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* buffer; the \" escape code is handled. Multiple strings
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* on one line are handled.
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*/
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unsigned readbuffer(FILE *input, unsigned char *buffer)
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{
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char str[256];
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unsigned buffersize;
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int i,linenr;
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linenr=0;
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buffersize=0;
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rewind(input);
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while (!feof(input)) {
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while (fgets(str,sizeof str,input)!=NULL) {
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linenr++;
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check_tablename(str);
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check_separator(str);
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if (strmatch(str,START_TOKEN,NULL))
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break;
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} /* while */
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if (!strmatch(str,START_TOKEN,NULL))
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return buffersize; /* no (more) section found, quit */
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while (fgets(str,sizeof str,input)!=NULL) {
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linenr++;
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check_if(str,linenr);
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if (check_tablename(str))
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printf("Error: table name definition should not be in SCPACK section (line %d)\n", linenr);
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check_separator(str);
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if (strmatch(str,"#else",NULL))
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break; /* done */
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/* add to the buffer only what is between double quotes */
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i=0;
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do {
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while (str[i]!='\0' && str[i]!='"')
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i++;
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if (str[i]=='"') {
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/* we are in a string */
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i++;
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while (str[i]!='\0' && str[i]!='"') {
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/* handle escape sequences */
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if (str[i]=='\\') {
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i++;
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switch (str[i]) {
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case 'a': /* alarm */
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buffer[buffersize++]='\a';
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i++;
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break;
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case 'b': /* backspace */
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buffer[buffersize++]='\b';
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i++;
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break;
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case 'f': /* form feed */
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buffer[buffersize++]='\f';
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i++;
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break;
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case 'n': /* newline */
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buffer[buffersize++]='\n';
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i++;
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break;
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case 'r': /* carriage return */
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buffer[buffersize++]='\n';
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i++;
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break;
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case 't': /* tab */
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buffer[buffersize++]='\t';
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i++;
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break;
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case '\'':
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buffer[buffersize++]='\'';
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i++;
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break;
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case '"':
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buffer[buffersize++]='"';
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i++;
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break;
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default:
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// ??? octal character code escapes and hexadecimal escapes
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// not supported
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printf("Unknown escape sequence '\\%c' on line %d\n",
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str[i], linenr);
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} /* switch */
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} else {
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buffer[buffersize++]=str[i++];
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} /* if */
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} /* while */
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if (str[i]=='"') {
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buffer[buffersize++]='\0'; /* terminate each string */
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i++;
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} else {
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printf("Error: unterminated string on line %d\n",linenr);
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} /* if */
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} /* if */
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} while (str[i]!='\0');
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} /* while - in SCPACK section */
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/* put in another '\0' to terminate the section */
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buffer[buffersize++]='\0';
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} /* while - !feof(input) */
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return buffersize;
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}
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static void write_pairtable(FILE *output, unsigned char pairtable[128][2], char *tablename)
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{
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int i;
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/* dump the pair table */
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fprintf(output, "/*-*SCPACK start of pair table, do not change or remove this line */\n");
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fprintf(output, "unsigned char %s[][2] = {", tablename);
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for (i=0; i<128 && pairtable[i][0]!=0 && pairtable[i][1]!=0; i++) {
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if ((i % 16)==0)
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fprintf(output, "\n ");
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else
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fprintf(output, " ");
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fprintf(output, "{%d,%d}", pairtable[i][0], pairtable[i][1]);
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/* check if something follows this pair */
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if (i+1<128 && pairtable[i+1][0]!=0 && pairtable[i+1][1]!=0)
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fprintf(output, ",");
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} /* for */
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fprintf(output, "\n};\n");
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fprintf(output, "/*-*SCPACK end of pair table, do not change or remove this line */\n");
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}
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void writefile(FILE *input, FILE *output, unsigned char *buffer, unsigned buffersize, unsigned char pairtable[128][2])
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{
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char str[256];
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int insection, indent, needseparator;
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unsigned char *bufptr;
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bufptr = buffer;
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insection = 0;
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rewind(input);
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while (!feof(input)) {
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while (fgets(str,sizeof str,input)!=NULL) {
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fprintf(output,"%s",str);
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if (check_tablename(str)) {
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write_pairtable(output, pairtable, tablename);
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/* strip an existing pair table from the file */
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if (fgets(str,sizeof str,input)!=NULL) {
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if (strmatch(str,"/*-*SCPACK",NULL)) {
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while (fgets(str,sizeof str,input)!=NULL)
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if (strmatch(str,"/*-*SCPACK",NULL))
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break;
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} else {
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fprintf(output,"%s",str);
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} /* if */
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} /* if */
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} /* if */
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if (strmatch(str,START_TOKEN,NULL))
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insection = 1;
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if (insection && strmatch(str,"#else",NULL))
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break;
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} /* while */
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if (!strmatch(str,"#else",&indent))
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return; /* no (more) section found, quit */
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insection=0;
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/* dump the buffer as strings, separated with commas */
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needseparator = 0;
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while (*bufptr != '\0') {
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assert((unsigned)(bufptr-buffer) < buffersize);
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if (needseparator)
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fprintf(output, "%s\n",separator);
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fprintf(output, "%*c\"",indent+2,' ');
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/* loop over string */
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while (*bufptr != '\0') {
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if (*bufptr<' ' || *bufptr >= 128 || *bufptr == '"' || *bufptr == '\\')
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fprintf(output, "\\%03o", *bufptr);
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else
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fprintf(output, "%c", *bufptr);
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bufptr++;
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} /* while */
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fprintf(output, "\"");
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needseparator = 1;
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bufptr++; /* skip '\0' */
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} /* while */
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fprintf(output, "%s\n",terminator);
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bufptr++;
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/* skip the input file until the #endif section */
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while (fgets(str,sizeof str,input)!=NULL) {
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if (strmatch(str,"#endif",NULL)) {
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fprintf(output,"%s",str);
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break; /* done */
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} /* if */
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} /* while */
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} /* while - !feof(input) */
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}
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static void usage(void)
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{
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printf("Usage: scpack <filename> [output file]\n");
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exit(1);
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}
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int main(int argc, char **argv)
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{
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FILE *in, *out;
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unsigned char *buffer;
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unsigned buffersize, orgbuffersize;
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unsigned char pairtable[128][2];
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if (argc < 2 || argc > 3)
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usage();
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if ((in=fopen(argv[1],"rt"))==NULL) {
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printf("SCPACK: error opening input %s\n",argv[1]);
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usage();
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} /* if */
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if (argc == 2) {
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if ((out=fopen(TEMPFILE,"wt"))==NULL) {
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printf("SCPACK: error opening temporary file %s\n",TEMPFILE);
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usage();
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} /* if */
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} else {
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if ((out=fopen(argv[2],"wt"))==NULL) {
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printf("SCPACK: error opening output file %s\n",argv[2]);
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usage();
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} /* if */
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} /* if */
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buffer = (unsigned char *)malloc(MAXSIZE);
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if (buffer == NULL) {
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printf("SCPACK: error allocating memory\n");
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return 1;
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} /* if */
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/* 1. read the buffer
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* 2. compress the buffer
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* 3. copy the file, insert the compressed buffer
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*/
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buffersize = readbuffer(in, buffer);
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orgbuffersize = buffersize;
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if (buffersize > 0) {
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buffersize = compress(buffer, buffersize, pairtable);
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writefile(in, out, buffer, buffersize, pairtable);
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printf("SCPACK: compression ratio: %ld%% (%d -> %d)\n",
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100L-(100L*buffersize)/orgbuffersize, orgbuffersize, buffersize);
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} else {
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printf("SCPACK: no SCPACK section found, nothing to do\n");
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} /* if */
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fclose(out);
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fclose(in);
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/* let the new file replace the old file */
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if (buffersize == 0) {
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if (argc == 2)
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remove(TEMPFILE);
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else
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remove(argv[2]);
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} else if (argc == 2) {
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remove(argv[1]);
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rename(TEMPFILE,argv[1]);
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} /* if */
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return 0;
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}
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