FreeCalypso > hg > gsm-codec-lib
view libgsmefr/pow2.c @ 150:da17c7f02c6c
gsmefr-etsi-dec: add BE support
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Wed, 14 Dec 2022 22:04:39 +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); }