| /*********************************************************** |
| Copyright 1992 by Stichting Mathematisch Centrum, Amsterdam, The |
| Netherlands. |
| |
| All Rights Reserved |
| |
| Permission to use, copy, modify, and distribute this software and its |
| documentation for any purpose and without fee is hereby granted, |
| provided that the above copyright notice appear in all copies and that |
| both that copyright notice and this permission notice appear in |
| supporting documentation, and that the names of Stichting Mathematisch |
| Centrum or CWI not be used in advertising or publicity pertaining to |
| distribution of the software without specific, written prior permission. |
| |
| STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO |
| THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND |
| FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE |
| FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES |
| WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN |
| ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT |
| OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. |
| |
| ******************************************************************/ |
| |
| /* |
| ** Intel/DVI ADPCM coder/decoder. |
| ** |
| ** The algorithm for this coder was taken from the IMA Compatability Project |
| ** proceedings, Vol 2, Number 2; May 1992. |
| ** |
| ** Version 1.2, 18-Dec-92. |
| ** |
| ** Change log: |
| ** - Fixed a stupid bug, where the delta was computed as |
| ** stepsize*code/4 in stead of stepsize*(code+0.5)/4. |
| ** - There was an off-by-one error causing it to pick |
| ** an incorrect delta once in a blue moon. |
| ** - The NODIVMUL define has been removed. Computations are now always done |
| ** using shifts, adds and subtracts. It turned out that, because the standard |
| ** is defined using shift/add/subtract, you needed bits of fixup code |
| ** (because the div/mul simulation using shift/add/sub made some rounding |
| ** errors that real div/mul don't make) and all together the resultant code |
| ** ran slower than just using the shifts all the time. |
| ** - Changed some of the variable names to be more meaningful. |
| */ |
| |
| #include "adpcm.h" |
| #include <stdio.h> /*DBG*/ |
| |
| #ifndef __STDC__ |
| #define signed |
| #endif |
| |
| /* Intel ADPCM step variation table */ |
| static int indexTable[16] = { |
| -1, -1, -1, -1, 2, 4, 6, 8, |
| -1, -1, -1, -1, 2, 4, 6, 8, |
| }; |
| |
| static int stepsizeTable[89] = { |
| 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, |
| 19, 21, 23, 25, 28, 31, 34, 37, 41, 45, |
| 50, 55, 60, 66, 73, 80, 88, 97, 107, 118, |
| 130, 143, 157, 173, 190, 209, 230, 253, 279, 307, |
| 337, 371, 408, 449, 494, 544, 598, 658, 724, 796, |
| 876, 963, 1060, 1166, 1282, 1411, 1552, 1707, 1878, 2066, |
| 2272, 2499, 2749, 3024, 3327, 3660, 4026, 4428, 4871, 5358, |
| 5894, 6484, 7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899, |
| 15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794, 32767 |
| }; |
| |
| void |
| adpcm_coder(indata, outdata, len, state) |
| short indata[]; |
| char outdata[]; |
| int len; |
| struct adpcm_state *state; |
| { |
| short *inp; /* Input buffer pointer */ |
| signed char *outp; /* output buffer pointer */ |
| int val; /* Current input sample value */ |
| int sign; /* Current adpcm sign bit */ |
| int delta; /* Current adpcm output value */ |
| int diff; /* Difference between val and valprev */ |
| int step; /* Stepsize */ |
| int valpred; /* Predicted output value */ |
| int vpdiff; /* Current change to valpred */ |
| int index; /* Current step change index */ |
| int outputbuffer; /* place to keep previous 4-bit value */ |
| int bufferstep; /* toggle between outputbuffer/output */ |
| |
| outp = (signed char *)outdata; |
| inp = indata; |
| |
| valpred = state->valprev; |
| index = state->index; |
| step = stepsizeTable[index]; |
| |
| bufferstep = 1; |
| |
| for ( ; len > 0 ; len-- ) { |
| val = *inp++; |
| |
| /* Step 1 - compute difference with previous value */ |
| diff = val - valpred; |
| sign = (diff < 0) ? 8 : 0; |
| if ( sign ) diff = (-diff); |
| |
| /* Step 2 - Divide and clamp */ |
| /* Note: |
| ** This code *approximately* computes: |
| ** delta = diff*4/step; |
| ** vpdiff = (delta+0.5)*step/4; |
| ** but in shift step bits are dropped. The net result of this is |
| ** that even if you have fast mul/div hardware you cannot put it to |
| ** good use since the fixup would be too expensive. |
| */ |
| delta = 0; |
| vpdiff = (step >> 3); |
| |
| if ( diff >= step ) { |
| delta = 4; |
| diff -= step; |
| vpdiff += step; |
| } |
| step >>= 1; |
| if ( diff >= step ) { |
| delta |= 2; |
| diff -= step; |
| vpdiff += step; |
| } |
| step >>= 1; |
| if ( diff >= step ) { |
| delta |= 1; |
| vpdiff += step; |
| } |
| |
| /* Step 3 - Update previous value */ |
| if ( sign ) |
| valpred -= vpdiff; |
| else |
| valpred += vpdiff; |
| |
| /* Step 4 - Clamp previous value to 16 bits */ |
| if ( valpred > 32767 ) |
| valpred = 32767; |
| else if ( valpred < -32768 ) |
| valpred = -32768; |
| |
| /* Step 5 - Assemble value, update index and step values */ |
| delta |= sign; |
| |
| index += indexTable[delta]; |
| if ( index < 0 ) index = 0; |
| if ( index > 88 ) index = 88; |
| step = stepsizeTable[index]; |
| |
| /* Step 6 - Output value */ |
| if ( bufferstep ) { |
| outputbuffer = (delta << 4) & 0xf0; |
| } else { |
| *outp++ = (delta & 0x0f) | outputbuffer; |
| } |
| bufferstep = !bufferstep; |
| } |
| |
| /* Output last step, if needed */ |
| if ( !bufferstep ) |
| *outp++ = outputbuffer; |
| |
| state->valprev = valpred; |
| state->index = index; |
| } |
| |
| void |
| adpcm_decoder(indata, outdata, len, state) |
| char indata[]; |
| short outdata[]; |
| int len; |
| struct adpcm_state *state; |
| { |
| signed char *inp; /* Input buffer pointer */ |
| short *outp; /* output buffer pointer */ |
| int sign; /* Current adpcm sign bit */ |
| int delta; /* Current adpcm output value */ |
| int step; /* Stepsize */ |
| int valpred; /* Predicted value */ |
| int vpdiff; /* Current change to valpred */ |
| int index; /* Current step change index */ |
| int inputbuffer; /* place to keep next 4-bit value */ |
| int bufferstep; /* toggle between inputbuffer/input */ |
| |
| outp = outdata; |
| inp = (signed char *)indata; |
| |
| valpred = state->valprev; |
| index = state->index; |
| step = stepsizeTable[index]; |
| |
| bufferstep = 0; |
| |
| for ( ; len > 0 ; len-- ) { |
| |
| /* Step 1 - get the delta value */ |
| if ( bufferstep ) { |
| delta = inputbuffer & 0xf; |
| } else { |
| inputbuffer = *inp++; |
| delta = (inputbuffer >> 4) & 0xf; |
| } |
| bufferstep = !bufferstep; |
| |
| /* Step 2 - Find new index value (for later) */ |
| index += indexTable[delta]; |
| if ( index < 0 ) index = 0; |
| if ( index > 88 ) index = 88; |
| |
| /* Step 3 - Separate sign and magnitude */ |
| sign = delta & 8; |
| delta = delta & 7; |
| |
| /* Step 4 - Compute difference and new predicted value */ |
| /* |
| ** Computes 'vpdiff = (delta+0.5)*step/4', but see comment |
| ** in adpcm_coder. |
| */ |
| vpdiff = step >> 3; |
| if ( delta & 4 ) vpdiff += step; |
| if ( delta & 2 ) vpdiff += step>>1; |
| if ( delta & 1 ) vpdiff += step>>2; |
| |
| if ( sign ) |
| valpred -= vpdiff; |
| else |
| valpred += vpdiff; |
| |
| /* Step 5 - clamp output value */ |
| if ( valpred > 32767 ) |
| valpred = 32767; |
| else if ( valpred < -32768 ) |
| valpred = -32768; |
| |
| /* Step 6 - Update step value */ |
| step = stepsizeTable[index]; |
| |
| /* Step 7 - Output value */ |
| *outp++ = valpred; |
| } |
| |
| state->valprev = valpred; |
| state->index = index; |
| } |