ref: 321dbca6e023b24620df303b5e71e05ca0e46684
parent: 70ae0bcb338d941527573539e85ec30dddf9fc18
author: rrt <rrt>
date: Mon Dec 18 17:21:46 EST 2006
Re-add over-zealously excised lookup-table generation code.
--- a/src/g711.c
+++ b/src/g711.c
@@ -2151,6 +2151,216 @@
/* The following code was used to generate the lookup tables */
#ifdef GENERATE_TABLES
+
+#define SIGN_BIT (0x80) /* Sign bit for a A-law byte. */
+#define QUANT_MASK (0xf) /* Quantization field mask. */
+#define NSEGS (8) /* Number of A-law segments. */
+#define SEG_SHIFT (4) /* Left shift for segment number. */
+#define SEG_MASK (0x70) /* Segment field mask. */
+
+static int16_t seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF,+ 0x1FF, 0x3FF, 0x7FF, 0xFFF};
+static int16_t seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF,+ 0x3FF, 0x7FF, 0xFFF, 0x1FFF};
+
+static int16_t search(
+ int16_t val,
+ int16_t *table,
+ int size)
+{+ int i;
+
+ for (i = 0; i < size; i++) {+ if (val <= *table++)
+ return (i);
+ }
+ return (size);
+}
+
+/*
+ * linear2alaw() accepts an 13-bit signed integer and encodes it as A-law data
+ * stored in a unsigned char. This function should only be called with
+ * the data shifted such that it only contains information in the lower
+ * 13-bits.
+ *
+ * Linear Input Code Compressed Code
+ * ------------------------ ---------------
+ * 0000000wxyza 000wxyz
+ * 0000001wxyza 001wxyz
+ * 000001wxyzab 010wxyz
+ * 00001wxyzabc 011wxyz
+ * 0001wxyzabcd 100wxyz
+ * 001wxyzabcde 101wxyz
+ * 01wxyzabcdef 110wxyz
+ * 1wxyzabcdefg 111wxyz
+ *
+ * For further information see John C. Bellamy's Digital Telephony, 1982,
+ * John Wiley & Sons, pps 98-111 and 472-476.
+ */
+unsigned char st_13linear2alaw(
+ int16_t pcm_val) /* 2's complement (13-bit range) */
+{+ int16_t mask;
+ short seg;
+ unsigned char aval;
+
+ /* Have calling software do it since its already doing a shift
+ * from 32-bits down to 16-bits.
+ */
+ /* pcm_val = pcm_val >> 3; */
+
+ if (pcm_val >= 0) {+ mask = 0xD5; /* sign (7th) bit = 1 */
+ } else {+ mask = 0x55; /* sign bit = 0 */
+ pcm_val = -pcm_val - 1;
+ }
+
+ /* Convert the scaled magnitude to segment number. */
+ seg = search(pcm_val, seg_aend, 8);
+
+ /* Combine the sign, segment, and quantization bits. */
+
+ if (seg >= 8) /* out of range, return maximum value. */
+ return (unsigned char) (0x7F ^ mask);
+ else {+ aval = (unsigned char) seg << SEG_SHIFT;
+ if (seg < 2)
+ aval |= (pcm_val >> 1) & QUANT_MASK;
+ else
+ aval |= (pcm_val >> seg) & QUANT_MASK;
+ return (aval ^ mask);
+ }
+}
+
+/*
+ * alaw2linear() - Convert an A-law value to 16-bit signed linear PCM
+ *
+ */
+int16_t st_alaw2linear16(
+ unsigned char a_val)
+{+ int16_t t;
+ int16_t seg;
+
+ a_val ^= 0x55;
+
+ t = (a_val & QUANT_MASK) << 4;
+ seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;
+ switch (seg) {+ case 0:
+ t += 8;
+ break;
+ case 1:
+ t += 0x108;
+ break;
+ default:
+ t += 0x108;
+ t <<= seg - 1;
+ }
+ return ((a_val & SIGN_BIT) ? t : -t);
+}
+
+#define BIAS (0x84) /* Bias for linear code. */
+#define CLIP 8159
+
+/*
+ * linear2ulaw() accepts a 14-bit signed integer and encodes it as u-law data
+ * stored in a unsigned char. This function should only be called with
+ * the data shifted such that it only contains information in the lower
+ * 14-bits.
+ *
+ * In order to simplify the encoding process, the original linear magnitude
+ * is biased by adding 33 which shifts the encoding range from (0 - 8158) to
+ * (33 - 8191). The result can be seen in the following encoding table:
+ *
+ * Biased Linear Input Code Compressed Code
+ * ------------------------ ---------------
+ * 00000001wxyza 000wxyz
+ * 0000001wxyzab 001wxyz
+ * 000001wxyzabc 010wxyz
+ * 00001wxyzabcd 011wxyz
+ * 0001wxyzabcde 100wxyz
+ * 001wxyzabcdef 101wxyz
+ * 01wxyzabcdefg 110wxyz
+ * 1wxyzabcdefgh 111wxyz
+ *
+ * Each biased linear code has a leading 1 which identifies the segment
+ * number. The value of the segment number is equal to 7 minus the number
+ * of leading 0's. The quantization interval is directly available as the
+ * four bits wxyz. * The trailing bits (a - h) are ignored.
+ *
+ * Ordinarily the complement of the resulting code word is used for
+ * transmission, and so the code word is complemented before it is returned.
+ *
+ * For further information see John C. Bellamy's Digital Telephony, 1982,
+ * John Wiley & Sons, pps 98-111 and 472-476.
+ */
+unsigned char st_14linear2ulaw(
+ int16_t pcm_val) /* 2's complement (14-bit range) */
+{+ int16_t mask;
+ int16_t seg;
+ unsigned char uval;
+
+ /* Have calling software do it since its already doing a shift
+ * from 32-bits down to 16-bits.
+ */
+ /* pcm_val = pcm_val >> 2; */
+
+ /* Get the sign and the magnitude of the value. */
+ if (pcm_val < 0) {+ pcm_val = -pcm_val;
+ mask = 0x7F;
+ } else {+ mask = 0xFF;
+ }
+ if ( pcm_val > CLIP ) pcm_val = CLIP; /* clip the magnitude */
+ pcm_val += (BIAS >> 2);
+
+ /* Convert the scaled magnitude to segment number. */
+ seg = search(pcm_val, seg_uend, 8);
+
+ /*
+ * Combine the sign, segment, quantization bits;
+ * and complement the code word.
+ */
+ if (seg >= 8) /* out of range, return maximum value. */
+ return (unsigned char) (0x7F ^ mask);
+ else {+ uval = (unsigned char) (seg << 4) | ((pcm_val >> (seg + 1)) & 0xF);
+ return (uval ^ mask);
+ }
+
+}
+
+/*
+ * ulaw2linear() - Convert a u-law value to 16-bit linear PCM
+ *
+ * First, a biased linear code is derived from the code word. An unbiased
+ * output can then be obtained by subtracting 33 from the biased code.
+ *
+ * Note that this function expects to be passed the complement of the
+ * original code word. This is in keeping with ISDN conventions.
+ */
+int16_t st_ulaw2linear16(
+ unsigned char u_val)
+{+ int16_t t;
+
+ /* Complement to obtain normal u-law value. */
+ u_val = ~u_val;
+
+ /*
+ * Extract and bias the quantization bits. Then
+ * shift up by the segment number and subtract out the bias.
+ */
+ t = ((u_val & QUANT_MASK) << 3) + BIAS;
+ t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;
+
+ return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
+}
+
int main(void)
{int x, y, find2a = 0;