FreeCalypso > hg > gsm-codec-lib
view libgsmfr2/preprocess.c @ 479:616b7ba1135b
doc/AMR-library-API: document AMR-EFR hybrid decoder
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sun, 19 May 2024 22:22:40 +0000 |
parents | bd2271cb95d4 |
children |
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/* * This C source file has been adapted from TU-Berlin libgsm source, * original notice follows: * * 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. */ #include <stdint.h> #include <assert.h> #include "tw_gsmfr.h" #include "typedef.h" #include "ed_state.h" #include "ed_internal.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 ( struct gsmfr_0610_state * S, const 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; }