| /* ------------------------------------------------------------------ |
| * Copyright (C) 1998-2009 PacketVideo |
| * |
| * 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. |
| * ------------------------------------------------------------------- |
| */ |
| /**************************************************************************************** |
| Portions of this file are derived from the following 3GPP standard: |
| |
| 3GPP TS 26.073 |
| ANSI-C code for the Adaptive Multi-Rate (AMR) speech codec |
| Available from http://www.3gpp.org |
| |
| (C) 2004, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC) |
| Permission to distribute, modify and use this file under the standard license |
| terms listed above has been obtained from the copyright holder. |
| ****************************************************************************************/ |
| /* |
| |
| Pathname: ./audio/gsm-amr/c/src/sqrt_l.c |
| |
| ------------------------------------------------------------------------------ |
| REVISION HISTORY |
| |
| |
| Description: Updated template. Changed function interface to pass in a |
| pointer to overflow flag into the function instead of using a |
| global flag. Changed name of an input pointer from "exp" to "pExp" |
| for clarity. Removed inclusion of unwanted header files. |
| |
| Description: Removed inclusion of sqrt_l.tab file. Changed the array name |
| "table" to "sqrt_l_tbl". Fixed typos. |
| |
| Who: Date: |
| Description: |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| /*---------------------------------------------------------------------------- |
| ; INCLUDES |
| ----------------------------------------------------------------------------*/ |
| #include "sqrt_l.h" |
| #include "typedef.h" |
| #include "basic_op.h" |
| |
| /*---------------------------------------------------------------------------- |
| ; MACROS |
| ; Define module specific macros here |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; DEFINES |
| ; Include all pre-processor statements here. Include conditional |
| ; compile variables also. |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL FUNCTION DEFINITIONS |
| ; Function Prototype declaration |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /*---------------------------------------------------------------------------- |
| ; LOCAL STORE/BUFFER/POINTER DEFINITIONS |
| ; Variable declaration - defined here and used outside this module |
| ----------------------------------------------------------------------------*/ |
| |
| |
| /* |
| ------------------------------------------------------------------------------ |
| FUNCTION NAME: sqrt_l_exp |
| ------------------------------------------------------------------------------ |
| INPUT AND OUTPUT DEFINITIONS |
| |
| Inputs: |
| L_x = input value (Word32) |
| pExp = pointer to right shift to be applied to result |
| pOverflow = pointer to overflow flag |
| |
| Outputs: |
| pOverflow -> if the Inv_sqrt operation resulted in an overflow. |
| |
| Returns: |
| L_y = squareroot of L_x (Word32) |
| |
| Global Variables Used: |
| None. |
| |
| Local Variables Needed: |
| None. |
| |
| ------------------------------------------------------------------------------ |
| FUNCTION DESCRIPTION |
| |
| This function computes sqrt(L_x), where L_x is positive. |
| If L_var is negative or zero, the result is 0 |
| |
| 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 |
| |
| ------------------------------------------------------------------------------ |
| REQUIREMENTS |
| |
| None. |
| |
| ------------------------------------------------------------------------------ |
| REFERENCES |
| |
| sqrt_l.c, UMTS GSM AMR speech codec, R99 - Version 3.2.0, March 2, 2001 |
| |
| ------------------------------------------------------------------------------ |
| PSEUDO-CODE |
| |
| Word32 sqrt_l_exp ( // o : output value |
| Word32 L_x, // i : input value |
| Word16 *exp // o : right shift to be applied to result |
| ) |
| { |
| |
| // 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; |
| |
| if (L_x <= (Word32) 0) |
| { |
| *exp = 0; |
| return (Word32) 0; |
| } |
| |
| * The reference ETSI code uses a global Overflow flag. In the actual |
| * implementation a pointer to the overflow flag is passed into the function. |
| * This pointer is in turn passed into the basic math functions such as add(), |
| * L_shl(), L_shr(), sub() called by this module. |
| |
| e = norm_l (L_x) & 0xFFFE; // get next lower EVEN norm. exp |
| L_x = L_shl (L_x, e); // L_x is normalized to [0.25..1) |
| *exp = e; // 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; |
| |
| 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 |
| |
| return (L_y); |
| } |
| |
| ------------------------------------------------------------------------------ |
| RESOURCES USED [optional] |
| |
| When the code is written for a specific target processor the |
| the resources used should be documented below. |
| |
| HEAP MEMORY USED: x bytes |
| |
| STACK MEMORY USED: x bytes |
| |
| CLOCK CYCLES: (cycle count equation for this function) + (variable |
| used to represent cycle count for each subroutine |
| called) |
| where: (cycle count variable) = cycle count for [subroutine |
| name] |
| |
| ------------------------------------------------------------------------------ |
| CAUTION [optional] |
| [State any special notes, constraints or cautions for users of this function] |
| |
| ------------------------------------------------------------------------------ |
| */ |
| |
| Word32 sqrt_l_exp( /* o : output value, Q31 */ |
| Word32 L_x, /* i : input value, Q31 */ |
| Word16 *pExp, /* o : right shift to be applied to result, Q1 */ |
| Flag *pOverflow /* i : pointer to overflow flag */ |
| ) |
| |
| { |
| Word16 e; |
| Word16 i; |
| Word16 a; |
| Word16 tmp; |
| Word32 L_y; |
| |
| /* |
| 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) |
| */ |
| |
| if (L_x <= (Word32) 0) |
| { |
| *pExp = 0; |
| return (Word32) 0; |
| } |
| |
| e = norm_l(L_x) & 0xFFFE; /* get next lower EVEN norm. exp */ |
| L_x = L_shl(L_x, e, pOverflow); /* L_x is normalized to [0.25..1) */ |
| *pExp = e; /* return 2*exponent (or Q1) */ |
| |
| L_x >>= 10; |
| i = (Word16)(L_x >> 15) & 63; /* Extract b25-b31, 16<= i <=63 */ |
| /* because of normalization */ |
| |
| a = (Word16)(L_x); /* Extract b10-b24 */ |
| a &= (Word16) 0x7fff; |
| |
| if (i > 15) |
| { |
| i -= 16; /* 0 <= i <= 47 */ |
| } |
| |
| L_y = L_deposit_h(sqrt_l_tbl[i]); /* sqrt_l_tbl[i] << 16 */ |
| |
| /* sqrt_l_tbl[i] - sqrt_l_tbl[i+1]) */ |
| tmp = sub(sqrt_l_tbl[i], sqrt_l_tbl[i + 1], pOverflow); |
| |
| L_y = L_msu(L_y, tmp, a, pOverflow); /* L_y -= tmp*a*2 */ |
| |
| /* L_y = L_shr (L_y, *exp); */ /* denormalization done by caller */ |
| |
| return (L_y); |
| } |
| |
