| /* |
| ** Copyright 2003-2010, VisualOn, Inc. |
| ** |
| ** Licensed under the Apache License, Version 2.0 (the "License"); |
| ** you may not use this file except in compliance with the License. |
| ** You may obtain a copy of the License at |
| ** |
| ** http://www.apache.org/licenses/LICENSE-2.0 |
| ** |
| ** Unless required by applicable law or agreed to in writing, software |
| ** distributed under the License is distributed on an "AS IS" BASIS, |
| ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| ** See the License for the specific language governing permissions and |
| ** limitations under the License. |
| */ |
| |
| /*********************************************************************** |
| * * |
| * File : log2.c * |
| * Purpose : Computes log2(L_x) * |
| * * |
| ************************************************************************/ |
| |
| #include "log2.h" |
| /******************************************************************************** |
| * INCLUDE FILES |
| *********************************************************************************/ |
| #include "typedef.h" |
| #include "basic_op.h" |
| |
| /********************************************************************************* |
| * LOCAL VARIABLES AND TABLES |
| **********************************************************************************/ |
| #include "log2_tab.h" /* Table for Log2() */ |
| |
| /************************************************************************* |
| * |
| * FUNCTION: Log2_norm() |
| * |
| * PURPOSE: Computes log2(L_x, exp), where L_x is positive and |
| * normalized, and exp is the normalisation exponent |
| * If L_x is negative or zero, the result is 0. |
| * |
| * DESCRIPTION: |
| * The function Log2(L_x) is approximated by a table and linear |
| * interpolation. The following steps are used to compute Log2(L_x) |
| * |
| * 1- exponent = 30-norm_exponent |
| * 2- i = bit25-b31 of L_x; 32<=i<=63 (because of normalization). |
| * 3- a = bit10-b24 |
| * 4- i -=32 |
| * 5- fraction = table[i]<<16 - (table[i] - table[i+1]) * a * 2 |
| * |
| *************************************************************************/ |
| |
| void Log2_norm ( |
| Word32 L_x, /* (i) : input value (normalized) */ |
| Word16 exp, /* (i) : norm_l (L_x) */ |
| Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30) */ |
| Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ |
| ) |
| { |
| Word16 i, a, tmp; |
| Word32 L_y; |
| if (L_x <= (Word32) 0) |
| { |
| *exponent = 0; |
| *fraction = 0; |
| return; |
| } |
| *exponent = (30 - exp); |
| L_x = (L_x >> 9); |
| i = extract_h (L_x); /* Extract b25-b31 */ |
| L_x = (L_x >> 1); |
| a = (Word16)(L_x); /* Extract b10-b24 of fraction */ |
| a = (Word16)(a & (Word16)0x7fff); |
| i -= 32; |
| L_y = L_deposit_h (table[i]); /* table[i] << 16 */ |
| tmp = vo_sub(table[i], table[i + 1]); /* table[i] - table[i+1] */ |
| L_y = vo_L_msu (L_y, tmp, a); /* L_y -= tmp*a*2 */ |
| *fraction = extract_h (L_y); |
| |
| return; |
| } |
| |
| /************************************************************************* |
| * |
| * FUNCTION: Log2() |
| * |
| * PURPOSE: Computes log2(L_x), where L_x is positive. |
| * If L_x is negative or zero, the result is 0. |
| * |
| * DESCRIPTION: |
| * normalizes L_x and then calls Log2_norm(). |
| * |
| *************************************************************************/ |
| |
| void Log2 ( |
| Word32 L_x, /* (i) : input value */ |
| Word16 *exponent, /* (o) : Integer part of Log2. (range: 0<=val<=30) */ |
| Word16 *fraction /* (o) : Fractional part of Log2. (range: 0<=val<1) */ |
| ) |
| { |
| Word16 exp; |
| |
| exp = norm_l(L_x); |
| Log2_norm ((L_x << exp), exp, exponent, fraction); |
| } |
| |
| |
| |