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00026 #include "asterisk.h"
00027
00028 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 40722 $")
00029
00030 #include "asterisk/ulaw.h"
00031
00032 #define ZEROTRAP
00033 #define BIAS 0x84
00034 #define CLIP 32635
00035
00036 unsigned char __ast_lin2mu[16384];
00037 short __ast_mulaw[256];
00038
00039
00040 static unsigned char linear2ulaw(short sample)
00041 {
00042 static int exp_lut[256] = {
00043 0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
00044 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
00045 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
00046 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
00047 6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
00048 6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
00049 6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
00050 6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
00051 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00052 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00053 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00054 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00055 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00056 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00057 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
00058 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7 };
00059 int sign, exponent, mantissa;
00060 unsigned char ulawbyte;
00061
00062
00063 sign = (sample >> 8) & 0x80;
00064 if (sign != 0)
00065 sample = -sample;
00066 if (sample > CLIP)
00067 sample = CLIP;
00068
00069
00070 sample = sample + BIAS;
00071 exponent = exp_lut[(sample >> 7) & 0xFF];
00072 mantissa = (sample >> (exponent + 3)) & 0x0F;
00073 ulawbyte = ~(sign | (exponent << 4) | mantissa);
00074 #ifdef ZEROTRAP
00075 if (ulawbyte == 0)
00076 ulawbyte = 0x02;
00077 #endif
00078
00079 return ulawbyte;
00080 }
00081
00082
00083
00084
00085 void ast_ulaw_init(void)
00086 {
00087 int i;
00088 for (i = 0; i < 256; i++) {
00089 short mu, e, f, y;
00090 static short etab[] = {0,132,396,924,1980,4092,8316,16764};
00091
00092 mu = 255 - i;
00093 e = (mu & 0x70) / 16;
00094 f = mu & 0x0f;
00095 y = f * (1 << (e + 3));
00096 y += etab[e];
00097 if (mu & 0x80)
00098 y = -y;
00099 __ast_mulaw[i] = y;
00100 }
00101
00102 for (i = -32768; i < 32768; i++) {
00103 __ast_lin2mu[((unsigned short)i) >> 2] = linear2ulaw(i);
00104 }
00105 }
00106