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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 : inv_sqrt.h
- * Purpose : Computes 1/sqrt(L_x), where L_x is positive.
- * : If L_x is negative or zero, the result is
- * : 1 (3fff ffff).
- * Description : The function 1/sqrt(L_x) is approximated by a table
- * : and linear interpolation. The inverse square root is
- * : computed using the following steps:
- * 1- Normalization of L_x.
- * 2- If (30-exponent) is even then shift right once.
- * 3- exponent = (30-exponent)/2 +1
- * 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- L_y >>= exponent
- *
- ********************************************************************************
- */
- #ifndef inv_sqrt_h
- #define inv_sqrt_h "$Id $"
-
- /*
- ********************************************************************************
- * INCLUDE FILES
- ********************************************************************************
- */
- #include "typedef.h"
- /*
- ********************************************************************************
- * DEFINITION OF DATA TYPES
- ********************************************************************************
- */
-
- /*
- ********************************************************************************
- * DECLARATION OF PROTOTYPES
- ********************************************************************************
- */
-
- Word32 Inv_sqrt_ex ( /* (o) : output value (range: 0<=val<1) */
- Word32 L_x /* (i) : input value (range: 0<=val<=7fffffff) */
- );
-
- #endif
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