1/* 2 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische 3 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for 4 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE. 5 */ 6 7#include <stdio.h> 8#include <assert.h> 9 10#include "gsm610_priv.h" 11 12/* 4.2.0 .. 4.2.3 PREPROCESSING SECTION 13 * 14 * After A-law to linear conversion (or directly from the 15 * Ato D converter) the following scaling is assumed for 16 * input to the RPE-LTP algorithm: 17 * 18 * in: 0.1.....................12 19 * S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.* 20 * 21 * Where S is the sign bit, v a valid bit, and * a "don't care" bit. 22 * The original signal is called sop[..] 23 * 24 * out: 0.1................... 12 25 * S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0 26 */ 27 28 29void Gsm_Preprocess ( 30 struct gsm_state * S, 31 int16_t * s, 32 int16_t * so) /* [0..159] IN/OUT */ 33{ 34 35 int16_t z1 = S->z1 ; 36 int32_t L_z2 = S->L_z2 ; 37 int16_t mp = S->mp ; 38 39 int16_t s1 ; 40 int32_t L_s2 ; 41 42 int32_t L_temp ; 43 44 int16_t msp, lsp ; 45 int16_t SO ; 46 47 register int k = 160 ; 48 49 while (k--) 50 { 51 52 /* 4.2.1 Downscaling of the input signal */ 53 SO = arith_shift_left (SASR_W (*s, 3), 2) ; 54 s++ ; 55 56 assert (SO >= -0x4000) ; /* downscaled by */ 57 assert (SO <= 0x3FFC) ; /* previous routine. */ 58 59 60 /* 4.2.2 Offset compensation 61 * 62 * This part implements a high-pass filter and requires extended 63 * arithmetic precision for the recursive part of this filter. 64 * The input of this procedure is the array so[0...159] and the 65 * output the array sof[ 0...159 ]. 66 */ 67 68 /* Compute the non-recursive part */ 69 70 s1 = SO - z1 ; /* s1 = gsm_sub (*so, z1) ; */ 71 z1 = SO ; 72 73 assert (s1 != MIN_WORD) ; 74 75 /* Compute the recursive part */ 76 L_s2 = s1 ; 77 L_s2 = arith_shift_left (L_s2, 15) ; 78 79 /* Execution of a 31 bv 16 bits multiplication */ 80 81 msp = SASR_L (L_z2, 15) ; 82 lsp = L_z2 - arith_shift_left ((int32_t) msp, 15) ; /* gsm_L_sub (L_z2,(msp<<15)) ; */ 83 84 L_s2 += GSM_MULT_R (lsp, 32735) ; 85 L_temp = (int32_t) msp * 32735 ; /* GSM_L_MULT (msp,32735) >> 1 ;*/ 86 L_z2 = GSM_L_ADD (L_temp, L_s2) ; 87 88 /* Compute sof[k] with rounding */ 89 L_temp = GSM_L_ADD (L_z2, 16384) ; 90 91 /* 4.2.3 Preemphasis */ 92 93 msp = GSM_MULT_R (mp, -28180) ; 94 mp = SASR_L (L_temp, 15) ; 95 *so++ = GSM_ADD (mp, msp) ; 96 } 97 98 S->z1 = z1 ; 99 S->L_z2 = L_z2 ; 100 S->mp = mp ; 101} 102