FreeCalypso > hg > gsm-codec-lib
view libtwamr/sqrt_l.c @ 491:45bf34451dd7
libgsmhr1: implement TW-TS-002 input
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 15 Jun 2024 06:22:21 +0000 |
parents | 8dfb7cbe6b59 |
children |
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/* ******************************************************************************** * * GSM AMR-NB speech codec R98 Version 7.6.0 December 12, 2001 * R99 Version 3.3.0 * REL-4 Version 4.1.0 * ******************************************************************************** * * File : sqrt_l.c * Purpose : Computes sqrt(L_x), where L_x is positive. * : If L_var is negative or zero, the result is 0 * Description : * The function sqrt(L_x) is approximated by a table and linear * interpolation. The square root is computed using the * following steps: * 1- Normalization of L_x. * 2- If exponent is even then shift right once. * 3- exponent = exponent/2 * 4- i = bit25-b31 of L_x; 16<=i<=63 because of normalization. * 5- a = bit10-b24 * 6- i -=16 * 7- L_y = table[i]<<16 - (table[i] - table[i+1]) * a * 2 * 8- return L_y and exponent so caller can do denormalization * ******************************************************************************** */ /* ******************************************************************************** * MODULE INCLUDE FILE AND VERSION ID ******************************************************************************** */ #include "namespace.h" #include "sqrt_l.h" /* ******************************************************************************** * INCLUDE FILES ******************************************************************************** */ #include "typedef.h" #include "basic_op.h" #include "no_count.h" /* ******************************************************************************** * LOCAL VARIABLES AND TABLES ******************************************************************************** */ #include "sqrt_l.tab" /* Table for sqrt_l_exp() */ /* ******************************************************************************** * PUBLIC PROGRAM CODE ******************************************************************************** */ Word32 sqrt_l_exp (/* o : output value, Q31 */ Word32 L_x, /* i : input value, Q31 */ Word16 *exp /* o : right shift to be applied to result, Q1 */ ) { /* y = sqrt(x) x = f * 2^-e, 0.5 <= f < 1 (normalization) y = sqrt(f) * 2^(-e/2) a) e = 2k --> y = sqrt(f) * 2^-k (k = e div 2, 0.707 <= sqrt(f) < 1) b) e = 2k+1 --> y = sqrt(f/2) * 2^-k (k = e div 2, 0.5 <= sqrt(f/2) < 0.707) */ Word16 e, i, a, tmp; Word32 L_y; test (); if (L_x <= (Word32) 0) { *exp = 0; move16 (); return (Word32) 0; } e = norm_l (L_x) & 0xFFFE; logic16 (); /* get next lower EVEN norm. exp */ L_x = L_shl (L_x, e); /* L_x is normalized to [0.25..1) */ *exp = e; move16 (); /* return 2*exponent (or Q1) */ L_x = L_shr (L_x, 9); i = extract_h (L_x); /* Extract b25-b31, 16 <= i <= 63 because of normalization */ L_x = L_shr (L_x, 1); a = extract_l (L_x); /* Extract b10-b24 */ a = a & (Word16) 0x7fff; logic16 (); i = sub (i, 16); /* 0 <= i <= 47 */ L_y = L_deposit_h (table[i]); /* table[i] << 16 */ tmp = sub (table[i], table[i + 1]); /* table[i] - table[i+1]) */ L_y = L_msu (L_y, tmp, a); /* L_y -= tmp*a*2 */ /* L_y = L_shr (L_y, *exp); */ /* denormalization done by caller */ return (L_y); }