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thd_entropy16.c
Go to the documentation of this file.00001 /*--------------------------------------------------------------------*/ 00002 /*----- 02 Mar 2001 - RWCox - Used for AUTOGZIP decision -------------*/ 00003 00004 #include "mrilib.h" 00005 00006 #undef SNUM 00007 #define SNUM 65536 /* one for every possible 16 bit pattern */ 00008 00009 static int * scount=NULL ; /* holds count of unsigned shorts */ 00010 static int snum=0 ; /* total number of unsigned shorts processed */ 00011 00012 /*-----------------------------------------------------------------------*/ 00013 00014 void ENTROPY_setup(void) 00015 { 00016 if( scount == NULL ) scount = (int *) malloc(sizeof(int)*SNUM) ; 00017 memset( scount , 0 , sizeof(int)*SNUM ) ; 00018 snum = 0 ; 00019 } 00020 00021 /*-----------------------------------------------------------------------*/ 00022 00023 void ENTROPY_setdown(void) 00024 { 00025 if( scount != NULL ){ free(scount); scount = NULL; snum = 0; } 00026 } 00027 00028 /*-----------------------------------------------------------------------*/ 00029 00030 void ENTROPY_accumulate( int nbytes , void * var ) 00031 { 00032 int nn = nbytes/2 , ii ; 00033 unsigned short * sar = (unsigned short *) var ; 00034 00035 if( scount == NULL ) ENTROPY_setup() ; 00036 00037 for( ii=0 ; ii < nn ; ii++ ) scount[sar[ii]]++ ; 00038 snum += nn ; 00039 } 00040 00041 /*----------------------------------------------------------------------- 00042 Value returned is in bits per 16 bit unsigned short 00043 -------------------------------------------------------------------------*/ 00044 00045 double ENTROPY_compute(void) 00046 { 00047 register int ii ; 00048 register double sum ; 00049 00050 if( scount == NULL || snum == 0 ) return 0.0 ; 00051 00052 sum = 0.0 ; 00053 for( ii=0 ; ii < SNUM ; ii++ ) 00054 if( scount[ii] > 0 ) sum += scount[ii] * log((double)scount[ii]) ; 00055 00056 sum = -(sum - snum*log((double)snum)) / ( log(2.0) * snum ) ; 00057 return sum ; 00058 } 00059 00060 /*-----------------------------------------------------------------------*/ 00061 00062 double ENTROPY_dataset( THD_3dim_dataset * dset ) 00063 { 00064 if( !ISVALID_DSET(dset) ) return(0.0) ; 00065 DSET_load(dset) ; 00066 if( !DSET_LOADED(dset) ) return(0.0) ; 00067 return ENTROPY_datablock( dset->dblk ) ; 00068 } 00069 00070 /*-----------------------------------------------------------------------*/ 00071 00072 double ENTROPY_datablock( THD_datablock * blk ) 00073 { 00074 int iv ; 00075 double sum ; 00076 00077 ENTRY("ENTROPY_datablock") ; 00078 00079 ENTROPY_setup() ; 00080 00081 for( iv=0 ; iv < blk->nvals ; iv++ ) 00082 ENTROPY_accumulate( DBLK_BRICK_BYTES(blk,iv) , DBLK_ARRAY(blk,iv) ) ; 00083 00084 sum = ENTROPY_compute() ; 00085 ENTROPY_setdown() ; 00086 RETURN(sum) ; 00087 }
