diff options
Diffstat (limited to 'gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c')
-rw-r--r-- | gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c b/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c new file mode 100644 index 000000000..99c0709dc --- /dev/null +++ b/gr-gsm-fr-vocoder/src/lib/gsm/preprocess.c @@ -0,0 +1,113 @@ +/* + * 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. + */ + +/* $Header$ */ + +#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; +} |