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Diffstat (limited to 'media/libstagefright/codecs/amrnb/common/src/sqrt_l.cpp')
| -rw-r--r-- | media/libstagefright/codecs/amrnb/common/src/sqrt_l.cpp | 266 |
1 files changed, 266 insertions, 0 deletions
diff --git a/media/libstagefright/codecs/amrnb/common/src/sqrt_l.cpp b/media/libstagefright/codecs/amrnb/common/src/sqrt_l.cpp new file mode 100644 index 0000000..8f74aa6 --- /dev/null +++ b/media/libstagefright/codecs/amrnb/common/src/sqrt_l.cpp @@ -0,0 +1,266 @@ +/* ------------------------------------------------------------------ + * 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); +} + |