80 lines
1.7 KiB
C++
80 lines
1.7 KiB
C++
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#include <windows.h>
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#include "dsdmo.h"
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double LogNorm[32] =
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{
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1, 1, 1.5, 1, 1.75, 1.4, 1.17, 1, 1.88, 1.76, 1.5, 1.36, 1.25, 1.15, 1.07,
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1, 1.94, 1.82, 1.72, 1.63, 1.55, 1.48, 1.41, 1.35, 1.29, 1.24, 1.19, 1.15,
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1.11, 1.07, 1.03, 1
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};
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float mylog( float finput, unsigned long maxexponent)
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{
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unsigned long mantissa, exponent, exponentwidth ;
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long input, output, sign;
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#ifdef DONTUSEi386
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_asm {
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fld finput
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fistp input
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}
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#else
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input = (int)finput;
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#endif
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/*
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* Separate the sign bit
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*/
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sign = input & 0x80000000L ; /* Preserve sign */
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/*
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* Separate mantissa bits from the sign and
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* complement them if original input was negative
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*/
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mantissa = sign ? -input : input;
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/*
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* Attempt to normalize the input to form the mantissa and
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* thereby calculate the actual exponent.
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*/
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exponent = maxexponent ;
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while( (mantissa < 0x80000000) && (exponent > 0) ) {
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mantissa = mantissa << 1 ;
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exponent-- ;
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}
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/*
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* If normalization was successful, mask off the MSB (since it
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* will be implied by a non-zero exponent) and adjust the exponent value
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*/
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if( mantissa >= 0x80000000 ) {
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mantissa = mantissa & 0x7FFFFFFF ;
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exponent++ ;
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}
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/*
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* Find the width of the exponent field required to represent
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* maxeponent and assemble the sign, exponent and mantissa fields
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* based on that width.
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*/
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if( maxexponent > 15 )
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exponentwidth = 5 ;
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else if( maxexponent > 7 )
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exponentwidth = 4 ;
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else if( maxexponent > 3 )
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exponentwidth = 3 ;
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else
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exponentwidth = 2 ;
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if (sign == 0x80000000L)
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output = sign | ~((exponent << (31-exponentwidth)) | (mantissa >> exponentwidth)) ;
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else
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output = sign | ((exponent << (31-exponentwidth)) | (mantissa >> exponentwidth)) ;
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float x = (float)output;
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return(x);
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}
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