Doxygen Source Code Documentation
ent16.c File Reference
#include "mrilib.h"Go to the source code of this file.
Defines | |
| #define | NBUF 16384 |
Functions | |
| int | main (int argc, char *argv[]) |
Define Documentation
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Definition at line 3 of file ent16.c. Referenced by main(). |
Function Documentation
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\** File : SUMA.c
Input paramters :
Definition at line 5 of file ent16.c. References argc, ENTROPY_accumulate(), ENTROPY_compute(), ENTROPY_setdown(), ENTROPY_setup(), machdep(), NBUF, and strtod().
00006 {
00007 char buf[NBUF] ;
00008 int nn ; double ee,pp , cutper=0.0 ;
00009
00010 if( argc > 1 ){
00011 if( strcmp(argv[1],"-help") == 0 ){
00012 printf("Usage: ent16 [-%%nn]\n"
00013 "Computes an estimate of the entropy of stdin.\n"
00014 "If the flag '-%%75' is given (e.g.), then the\n"
00015 " exit status is 1 only if the input could be\n"
00016 " compressed at least 75%%, otherwise the exit\n"
00017 " status is 0. Legal values of 'nn' are 1..99.\n"
00018 "In any case, the entropy and compression estimates\n"
00019 " are printed to stdout, even if no '-%%nn' flag is.\n"
00020 " given.\n"
00021 "\n"
00022 "METHOD: entropy is estimated by building a histogram\n"
00023 " of all 16 bit words in the input, then summing\n"
00024 " over -p[i]*log2(p[i]), i=0..65535. Compression\n"
00025 " estimate seems to work pretty good for gzip -1\n"
00026 " in most cases of binary image data.\n"
00027 "\n"
00028 "SAMPLE USAGE (csh syntax):\n"
00029 " ent16 -%%75 < fred+orig.BRIK\n"
00030 " if( $status == 1 ) gzip -1v fred+orig.BRIK\n"
00031 ) ;
00032 exit(0) ;
00033
00034 } else if( strncmp(argv[1],"-%",2) == 0 ){
00035 cutper = strtod( argv[1]+2 , NULL ) ;
00036 if( cutper < 1.0 || cutper > 99.0 ) cutper = 0.0 ;
00037
00038 } else {
00039 fprintf(stderr,"++ ent16: Unknown option %s ignored!\n",argv[1]) ;
00040 }
00041 }
00042
00043 machdep() ;
00044
00045 /*--------------------------*/
00046
00047 ENTROPY_setup() ;
00048 do{
00049 nn = fread( buf , 1 , NBUF , stdin ) ;
00050 if( nn <= 0 ) break ;
00051 ENTROPY_accumulate( nn , buf ) ;
00052 } while(1) ;
00053
00054 /*--------------------------*/
00055
00056 ee = ENTROPY_compute() ; ENTROPY_setdown() ;
00057 pp = 100.0*(1.0-ee/16.0) ;
00058
00059 printf("entropy=%6.3f bits/word compression=%5.2f%%\n",
00060 ee , pp ) ;
00061
00062 if( cutper > 0.0 && pp >= cutper ) exit(1) ;
00063 exit(0) ;
00064 }
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