filebaseulaw.C

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#include "assets.h"
#include "byteorder.h"
#include "file.h"
#include "filebase.h"
#include "sizes.h"

// ======================================= ulaw codecs

float FileBase::ulawtofloat(char ulaw)
{
//printf("%f\n", ulawtofloat_ptr[ulaw]);
        return ulawtofloat_ptr[(unsigned char)ulaw];
}

char FileBase::floattoulaw(float value)
{
        return floattoulaw_ptr[(int)(value * 32767)];
}

// turn off the trap as per the MIL-STD
#undef ZEROTRAP
// define the add-in bias for 16 bit samples
#define uBIAS 0x84
#define uCLIP 32635

int FileBase::generate_ulaw_tables()
{
        int i;
        float value;

        if(!ulawtofloat_table)
        {
        static int exp_lut[8] = { 0, 132, 396, 924, 1980, 4092, 8316, 16764 };
        int sign, exponent, mantissa, sample;
                unsigned char ulawbyte;

                ulawtofloat_table = new float[256];
                ulawtofloat_ptr = ulawtofloat_table;
                for(i = 0; i < 256; i++)
                {
                        ulawbyte = (unsigned char)i;
                ulawbyte = ~ ulawbyte;
                sign = ( ulawbyte & 0x80 );
                exponent = ( ulawbyte >> 4 ) & 0x07;
                mantissa = ulawbyte & 0x0F;
                sample = exp_lut[exponent] + ( mantissa << ( exponent + 3 ) );
                if ( sign != 0 ) sample = -sample;

                        ulawtofloat_ptr[(int)i] = (float)sample / 32768;
                }
        }

        if(!floattoulaw_table)
        {
        int sign, exponent, mantissa;
        unsigned char ulawbyte;
                int sample;
        int exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
                               4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};

                floattoulaw_table = new unsigned char[65536];
                floattoulaw_ptr = floattoulaw_table + 32768;

                for(i = -32768; i < 32768; i++)
                {
                        sample = i;
// Get the sample into sign-magnitude.
                sign = (sample >> 8) & 0x80;            // set aside the sign
                if ( sign != 0 ) sample = -sample;              // get magnitude
                if ( sample > uCLIP ) sample = uCLIP;           // clip the magnitude

// Convert from 16 bit linear to ulaw.
                sample = sample + uBIAS;
                    exponent = exp_lut[( sample >> 7 ) & 0xFF];
                    mantissa = ( sample >> ( exponent + 3 ) ) & 0x0F;
                    ulawbyte = ~ ( sign | ( exponent << 4 ) | mantissa );
#ifdef ZEROTRAP
                    if ( ulawbyte == 0 ) ulawbyte = 0x02;       /* optional CCITT trap */
#endif

                    floattoulaw_ptr[i] = ulawbyte;
                }
        }
        return 0;
}

int FileBase::delete_ulaw_tables()
{
        if(floattoulaw_table) delete [] floattoulaw_table;
        if(ulawtofloat_table) delete [] ulawtofloat_table;
        floattoulaw_table = 0;
        ulawtofloat_table = 0;
        return 0;
}

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