1 files changed, 62 insertions, 20 deletions
diff --git a/libFDK/src/fixpoint_math.cpp b/libFDK/src/fixpoint_math.cpp
index 78cae2b..30283ff 100644
--- a/libFDK/src/fixpoint_math.cpp
+++ b/libFDK/src/fixpoint_math.cpp
@@ -242,30 +242,72 @@ FIXP_DBL mul_dbl_sgl_rnd (const FIXP_DBL op1, const FIXP_SGL op2)
 
 *****************************************************************************/
 LNK_SECTION_CODE_L1
-FIXP_DBL CalcInvLdData(FIXP_DBL op)
+/* This table is used for lookup 2^x with   */
+/* x in range [0...1.0[ in steps of 1/32 */
+LNK_SECTION_DATA_L1 static const UINT exp2_tab_long[32]={
+0x40000000,0x4166C34C,0x42D561B4,0x444C0740,
+0x45CAE0F2,0x47521CC6,0x48E1E9BA,0x4A7A77D4,
+0x4C1BF829,0x4DC69CDD,0x4F7A9930,0x51382182,
+0x52FF6B55,0x54D0AD5A,0x56AC1F75,0x5891FAC1,
+0x5A82799A,0x5C7DD7A4,0x5E8451D0,0x60962665,
+0x62B39509,0x64DCDEC3,0x6712460B,0x69540EC9,
+0x6BA27E65,0x6DFDDBCC,0x70666F76,0x72DC8374,
+0x75606374,0x77F25CCE,0x7A92BE8B,0x7D41D96E
+// 0x80000000
+};
+
+/* This table is used for lookup 2^x with   */
+/* x in range [0...1/32[ in steps of 1/1024 */
+LNK_SECTION_DATA_L1 static const UINT exp2w_tab_long[32]={
+0x40000000,0x400B1818,0x4016321B,0x40214E0C,
+0x402C6BE9,0x40378BB4,0x4042AD6D,0x404DD113,
+0x4058F6A8,0x40641E2B,0x406F479E,0x407A7300,
+0x4085A051,0x4090CF92,0x409C00C4,0x40A733E6,
+0x40B268FA,0x40BD9FFF,0x40C8D8F5,0x40D413DD,
+0x40DF50B8,0x40EA8F86,0x40F5D046,0x410112FA,
+0x410C57A2,0x41179E3D,0x4122E6CD,0x412E3152,
+0x41397DCC,0x4144CC3B,0x41501CA0,0x415B6EFB,
+// 0x4166C34C,
+};
+/* This table is used for lookup 2^x with   */
+/* x in range [0...1/1024[ in steps of 1/32768 */
+LNK_SECTION_DATA_L1 static const UINT exp2x_tab_long[32]={
+0x40000000,0x400058B9,0x4000B173,0x40010A2D,
+0x400162E8,0x4001BBA3,0x4002145F,0x40026D1B,
+0x4002C5D8,0x40031E95,0x40037752,0x4003D011,
+0x400428CF,0x4004818E,0x4004DA4E,0x4005330E,
+0x40058BCE,0x4005E48F,0x40063D51,0x40069613,
+0x4006EED5,0x40074798,0x4007A05B,0x4007F91F,
+0x400851E4,0x4008AAA8,0x4009036E,0x40095C33,
+0x4009B4FA,0x400A0DC0,0x400A6688,0x400ABF4F,
+//0x400B1818
+};
+
+LNK_SECTION_CODE_L1 FIXP_DBL CalcInvLdData(FIXP_DBL x)
 {
-  FIXP_DBL result_m;
+  int set_zero = (x <  FL2FXCONST_DBL(-31.0/64.0))? 0 : 1;
+  int set_max  = (x >= FL2FXCONST_DBL( 31.0/64.0)) | (x == FL2FXCONST_DBL(0.0));
 
-  if ( op == FL2FXCONST_DBL(0.0f) ) {
-    result_m = (FIXP_DBL)MAXVAL_DBL;
-  }
-  else if ( op < FL2FXCONST_DBL(0.0f) ) {
-    result_m = f2Pow(op, LD_DATA_SHIFT);
-  }
-  else {
-    int result_e;
+  FIXP_SGL frac = (FIXP_SGL)(LONG)(x & 0x3FF);
+  UINT index3 = (UINT)(LONG)(x >> 10) & 0x1F;
+  UINT index2 = (UINT)(LONG)(x >> 15) & 0x1F; 
+  UINT index1 = (UINT)(LONG)(x >> 20) & 0x1F;
+  int exp  = (x >  FL2FXCONST_DBL(0.0f)) ? (31 - (int)(x>>25)) : (int)(-(x>>25));
 
-    result_m = f2Pow(op, LD_DATA_SHIFT, &result_e);
-    result_e = fixMin(fixMax(result_e+1-(DFRACT_BITS-1), -(DFRACT_BITS-1)), (DFRACT_BITS-1)); /* rounding and saturation */
+  UINT lookup1 = exp2_tab_long[index1]*set_zero;
+  UINT lookup2 = exp2w_tab_long[index2];
+  UINT lookup3 = exp2x_tab_long[index3];
+  UINT lookup3f = lookup3 + (UINT)(LONG)fMultDiv2((FIXP_DBL)(0x0016302F),(FIXP_SGL)frac);
+  
+  UINT lookup12 = (UINT)(LONG)fMult((FIXP_DBL)lookup1,  (FIXP_DBL) lookup2);
+  UINT lookup   = (UINT)(LONG)fMult((FIXP_DBL)lookup12, (FIXP_DBL) lookup3f);
 
-    if ( (result_e>0) && ( result_m > (((FIXP_DBL)MAXVAL_DBL)>>result_e) ) ) {
-      result_m = (FIXP_DBL)MAXVAL_DBL; /* saturate to max representable value */
-    }
-    else {
-      result_m = (scaleValue(result_m, result_e)+(FIXP_DBL)1)>>1; /* descale result + rounding */
-    }
-  }
-  return result_m;
+  FIXP_DBL retVal = (lookup<<3) >> exp;
+
+  if (set_max)
+    retVal=FL2FXCONST_DBL(1.0f);
+
+  return retVal;
 }