FreeCalypso > hg > gsm-codec-lib
view libgsmefr/pow2.c @ 183:452c1d5a6268
libgsmefr BFI w/o data: emit zero output after decoder reset
In real-life usage, each EFR decoder session will most likely begin
with lots of BFI frames before the first real frame arrives. However,
because the spec-defined home state of the decoder is speech rather
than CN, our regular logic for BFI w/o data would have to feed
pseudorandom noise to the decoder (in the "fixed codebook excitation
pulses" part), which is silly to do at the beginning of the decoder
session right out of reset. Therefore, let's check reset_flag_old,
and if we are still in the reset state, simply emit zero output.
author | Mychaela Falconia <falcon@freecalypso.org> |
---|---|
date | Tue, 03 Jan 2023 00:12:18 +0000 |
parents | 33714b36841a |
children |
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/************************************************************************* * * FUNCTION: Pow2() * * PURPOSE: computes L_x = pow(2.0, exponent.fraction) * * DESCRIPTION: * The function Pow2(L_x) is approximated by a table and linear * interpolation. * 1- i = bit10-b15 of fraction, 0 <= i <= 31 * 2- a = bit0-b9 of fraction * 3- L_x = table[i]<<16 - (table[i] - table[i+1]) * a * 2 * 4- L_x = L_x >> (30-exponent) (with rounding) * *************************************************************************/ #include "gsm_efr.h" #include "typedef.h" #include "namespace.h" #include "basic_op.h" #include "no_count.h" #include "sig_proc.h" #include "pow2.tab" /* Table for Pow2() */ Word32 Pow2 ( /* (o) : result (range: 0<=val<=0x7fffffff) */ Word16 exponent, /* (i) : Integer part. (range: 0<=val<=30) */ Word16 fraction /* (i) : Fractional part. (range: 0.0<=val<1.0) */ ) { Word16 exp, i, a, tmp; Word32 L_x; L_x = L_mult (fraction, 32);/* L_x = fraction<<6 */ i = extract_h (L_x); /* Extract b10-b16 of fraction */ L_x = L_shr (L_x, 1); a = extract_l (L_x); /* Extract b0-b9 of fraction */ a = a & (Word16) 0x7fff; logic16 (); L_x = L_deposit_h (table[i]); /* table[i] << 16 */ tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1] */ L_x = L_msu (L_x, tmp, a); /* L_x -= tmp*a*2 */ exp = sub (30, exponent); L_x = L_shr_r (L_x, exp); return (L_x); }