cannam@154: /***********************************************************************
cannam@154: Copyright (c) 2006-2011, Skype Limited. All rights reserved.
cannam@154: Redistribution and use in source and binary forms, with or without
cannam@154: modification, are permitted provided that the following conditions
cannam@154: are met:
cannam@154: - Redistributions of source code must retain the above copyright notice,
cannam@154: this list of conditions and the following disclaimer.
cannam@154: - Redistributions in binary form must reproduce the above copyright
cannam@154: notice, this list of conditions and the following disclaimer in the
cannam@154: documentation and/or other materials provided with the distribution.
cannam@154: - Neither the name of Internet Society, IETF or IETF Trust, nor the
cannam@154: names of specific contributors, may be used to endorse or promote
cannam@154: products derived from this software without specific prior written
cannam@154: permission.
cannam@154: THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
cannam@154: AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
cannam@154: IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
cannam@154: ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
cannam@154: LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
cannam@154: CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
cannam@154: SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
cannam@154: INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
cannam@154: CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
cannam@154: ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
cannam@154: POSSIBILITY OF SUCH DAMAGE.
cannam@154: ***********************************************************************/
cannam@154: 
cannam@154: #ifdef HAVE_CONFIG_H
cannam@154: #include "config.h"
cannam@154: #endif
cannam@154: 
cannam@154: #include "SigProc_FIX.h"
cannam@154: 
cannam@154: /* Approximation of 2^() (very close inverse of silk_lin2log()) */
cannam@154: /* Convert input to a linear scale    */
cannam@154: opus_int32 silk_log2lin(
cannam@154:     const opus_int32            inLog_Q7            /* I  input on log scale                                            */
cannam@154: )
cannam@154: {
cannam@154:     opus_int32 out, frac_Q7;
cannam@154: 
cannam@154:     if( inLog_Q7 < 0 ) {
cannam@154:         return 0;
cannam@154:     } else if ( inLog_Q7 >= 3967 ) {
cannam@154:         return silk_int32_MAX;
cannam@154:     }
cannam@154: 
cannam@154:     out = silk_LSHIFT( 1, silk_RSHIFT( inLog_Q7, 7 ) );
cannam@154:     frac_Q7 = inLog_Q7 & 0x7F;
cannam@154:     if( inLog_Q7 < 2048 ) {
cannam@154:         /* Piece-wise parabolic approximation */
cannam@154:         out = silk_ADD_RSHIFT32( out, silk_MUL( out, silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) ), 7 );
cannam@154:     } else {
cannam@154:         /* Piece-wise parabolic approximation */
cannam@154:         out = silk_MLA( out, silk_RSHIFT( out, 7 ), silk_SMLAWB( frac_Q7, silk_SMULBB( frac_Q7, 128 - frac_Q7 ), -174 ) );
cannam@154:     }
cannam@154:     return out;
cannam@154: }