FreeCalypso > hg > gsm-codec-lib
view miscutil/pcm16-to-ulaw.c @ 251:946849291027
CHANGES: document changes since gsm-codec-lib-r1
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Fri, 12 May 2023 06:13:56 +0000 |
parents | c7f02428bda6 |
children |
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/* * This program reads a 16-bit PCM recording in raw format (robe by default, * or LE with -l option) and converts it to 8-bit PCM in North American * mu-law encoding. It is based on the ulaw_compress() function from ITU-T * G.191 STL, using the most significant 14 bits of each input linear PCM * sample, rather than just 13. A command line option is also provided * to truncate each input value to 13 bits prior to mu-law encoding, to * replicate the effect of using a table lookup conversion method that * only considers the upper 13 bits - specify -t option to select this mode. */ #include <stdio.h> #include <stdint.h> #include <stdlib.h> #include <string.h> #include <strings.h> #include <unistd.h> static unsigned ulaw_compress(input) unsigned input; { short i; /* aux.var. */ short absno; /* absolute value of linear (input) sample */ short segno; /* segment (Table 2/G711, column 1) */ short low_nibble; /* low nibble of log companded sample */ short high_nibble; /* high nibble of log companded sample */ unsigned output; /* -------------------------------------------------------------------- */ /* Input is 14-bit right-justified in this version */ /* Compute absolute value; adjust for easy processing */ /* -------------------------------------------------------------------- */ absno = input >= 0x2000 /* compute 1's complement in case of */ ? (~input & 0x1FFF) + 33 /* negative samples */ : input + 33; /* NB: 33 is the difference value */ /* between the thresholds for */ /* A-law and u-law. */ if (absno > (0x1FFF)) /* limitation to "absno" < 8192 */ absno = (0x1FFF); /* Determination of sample's segment */ i = absno >> 6; segno = 1; while (i != 0) { segno++; i >>= 1; } /* Mounting the high-nibble of the log-PCM sample */ high_nibble = (0x0008) - segno; /* Mounting the low-nibble of the log PCM sample */ low_nibble = (absno >> segno) /* right shift of mantissa and */ &(0x000F); /* masking away leading '1' */ low_nibble = (0x000F) - low_nibble; /* Joining the high-nibble and the low-nibble of the log PCM sample */ output = (high_nibble << 4) | low_nibble; /* Add sign bit */ if (input < 0x2000) output = output | (0x0080); return output; } main(argc, argv) char **argv; { int opt, little_endian = 0, truncate = 0; char *infname, *outfname; FILE *inf, *outf; uint8_t inb[2]; uint16_t ins; int cc; extern int optind; while ((opt = getopt(argc, argv, "lt")) != EOF) { switch (opt) { case 'l': little_endian = 1; continue; case 't': truncate = 1; continue; default: usage: fprintf(stderr, "usage: %s [-l] [-t] input.pcm16 output.ulaw\n", argv[0]); exit(1); } } if (argc != optind + 2) goto usage; infname = argv[optind]; outfname = argv[optind+1]; inf = fopen(infname, "r"); if (!inf) { perror(infname); exit(1); } outf = fopen(outfname, "w"); if (!outf) { perror(outfname); exit(1); } for (;;) { cc = fread(inb, 1, 2, inf); if (cc <= 0) break; if (cc & 1) { fprintf(stderr, "error: %s has odd number of bytes\n", infname); exit(1); } if (little_endian) ins = ((uint16_t) inb[1] << 8) | ((uint16_t) inb[0]); else ins = ((uint16_t) inb[0] << 8) | ((uint16_t) inb[1]); ins >>= 2; if (truncate) ins &= ~1; putc(ulaw_compress(ins), outf); } fclose(outf); exit(0); }