111 lines
2.8 KiB
C
111 lines
2.8 KiB
C
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/* INTIO.C - Routines to read and write integers one byte at a time. */
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/* Copyright (c) 1995-2012 by Radford M. Neal.
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*
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* Permission is granted for anyone to copy, use, modify, and distribute
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* these programs and accompanying documents for any purpose, provided
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* this copyright notice is retained and prominently displayed, and note
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* is made of any changes made to these programs. These programs and
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* documents are distributed without any warranty, express or implied.
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* As the programs were written for research purposes only, they have not
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* been tested to the degree that would be advisable in any important
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* application. All use of these programs is entirely at the user's own
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* risk.
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include "intio.h"
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/* READ AN INTEGER ONE BYTE AT A TIME. Four bytes are read, ordered from
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low to high order. These are considered to represent a signed integer,
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in two's complement form. The value returned is this integer, converted
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to whatever a C "int" is. The conversion should work as long as an "int"
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is at least four bytes, even if it's not in two's complement representation
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(except for the largest two's complement negative integer).
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If an error or eof is encountered, zero is returned. The caller can
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check for these events using feof and ferror.
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The file read from should have been opened as "binary".
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*/
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int intio_read
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( FILE *f /* File to read from */
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)
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{
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unsigned char b[4];
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int top;
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int i;
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for (i = 0; i<4; i++)
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{ if (fread(&b[i],1,1,f) != 1) return 0;
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}
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top = b[3]>127 ? (int)b[3] - 256 : b[3];
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return (top<<24) + (b[2]<<16) + (b[1]<<8) + b[0];
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}
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/* WRITE AN INTEGER ONE BYTE AT A TIME. Four bytes are written, ordered from
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low to high order. These are considered to represent a signed integer,
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in two's complement form. This should work as long as the integer passed
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can be represented in four bytes, even if a C "int" is longer than this.
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The file written to should have been opened as "binary".
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*/
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void intio_write
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( FILE *f, /* File to write to */
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int v /* Value to write to file */
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)
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{
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unsigned char b;
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int i;
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for (i = 0; i<3; i++)
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{ b = v&0xff;
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fwrite(&b,1,1,f);
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v >>= 8;
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}
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b = v>0 ? v : v+256;
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fwrite(&b,1,1,f);
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}
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/* TEST PROGRAM. */
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#ifdef TEST_INTIO
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main(void)
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{
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FILE *f;
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f = fopen("test","wb");
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intio_write(f,334);
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intio_write(f,-40000);
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intio_write(f,0x8fffffff);
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intio_write(f,-0x8fffffff);
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fclose(f);
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f = fopen("test","rb");
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if (intio_read(f)!=334
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|| intio_read(f)!=-40000
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|| intio_read(f)!=0x8fffffff
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|| intio_read(f)!=-0x8fffffff)
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{ fprintf(stderr,"got back bad data\n");
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exit(1);
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}
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if (intio_read(f)!=0 || !feof(f) || ferror(f))
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{ fprintf(stderr,"eof not handled correctly\n");
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exit(1);
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}
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fclose(f);
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fprintf(stderr,"OK\n");
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exit(0);
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}
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#endif
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