| /* |
| * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische |
| * Universitaet Berlin. See the accompanying file "COPYRIGHT" for |
| * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE. |
| */ |
| |
| /* $Header: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/preprocess.c,v 1.2 1994/05/10 20:18:45 jutta Exp $ */ |
| |
| #include "config.h" |
| #include <stdio.h> |
| #include <assert.h> |
| |
| #include "private.h" |
| |
| #include "gsm.h" |
| #include "proto.h" |
| |
| /* 4.2.0 .. 4.2.3 PREPROCESSING SECTION |
| * |
| * After A-law to linear conversion (or directly from the |
| * Ato D converter) the following scaling is assumed for |
| * input to the RPE-LTP algorithm: |
| * |
| * in: 0.1.....................12 |
| * S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.* |
| * |
| * Where S is the sign bit, v a valid bit, and * a "don't care" bit. |
| * The original signal is called sop[..] |
| * |
| * out: 0.1................... 12 |
| * S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0 |
| */ |
| |
| |
| void Gsm_Preprocess P3((S, s, so), |
| struct gsm_state * S, |
| word * s, |
| word * so ) /* [0..159] IN/OUT */ |
| { |
| |
| word z1 = S->z1; |
| longword L_z2 = S->L_z2; |
| word mp = S->mp; |
| |
| word s1; |
| longword L_s2; |
| |
| longword L_temp; |
| |
| word msp, lsp; |
| word SO; |
| |
| longword ltmp; /* for ADD */ |
| ulongword utmp; /* for L_ADD */ |
| |
| register int k = 160; |
| |
| while (k--) { |
| |
| /* 4.2.1 Downscaling of the input signal |
| */ |
| SO = SASR( *s, 3 ) << 2; |
| s++; |
| |
| assert (SO >= -0x4000); /* downscaled by */ |
| assert (SO <= 0x3FFC); /* previous routine. */ |
| |
| |
| /* 4.2.2 Offset compensation |
| * |
| * This part implements a high-pass filter and requires extended |
| * arithmetic precision for the recursive part of this filter. |
| * The input of this procedure is the array so[0...159] and the |
| * output the array sof[ 0...159 ]. |
| */ |
| /* Compute the non-recursive part |
| */ |
| |
| s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */ |
| z1 = SO; |
| |
| assert(s1 != MIN_WORD); |
| |
| /* Compute the recursive part |
| */ |
| L_s2 = s1; |
| L_s2 <<= 15; |
| |
| /* Execution of a 31 bv 16 bits multiplication |
| */ |
| |
| msp = SASR( L_z2, 15 ); |
| lsp = L_z2-((longword)msp<<15); /* gsm_L_sub(L_z2,(msp<<15)); */ |
| |
| L_s2 += GSM_MULT_R( lsp, 32735 ); |
| L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/ |
| L_z2 = GSM_L_ADD( L_temp, L_s2 ); |
| |
| /* Compute sof[k] with rounding |
| */ |
| L_temp = GSM_L_ADD( L_z2, 16384 ); |
| |
| /* 4.2.3 Preemphasis |
| */ |
| |
| msp = GSM_MULT_R( mp, -28180 ); |
| mp = SASR( L_temp, 15 ); |
| *so++ = GSM_ADD( mp, msp ); |
| } |
| |
| S->z1 = z1; |
| S->L_z2 = L_z2; |
| S->mp = mp; |
| } |