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1 // Copyright (c) 1995-2009 Nokia Corporation and/or its subsidiary(-ies). |
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2 // All rights reserved. |
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3 // This component and the accompanying materials are made available |
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4 // under the terms of the License "Symbian Foundation License v1.0" |
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5 // which accompanies this distribution, and is available |
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6 // at the URL "http://www.symbianfoundation.org/legal/sfl-v10.html". |
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7 // |
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8 // Initial Contributors: |
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9 // Nokia Corporation - initial contribution. |
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10 // |
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11 // Contributors: |
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12 // |
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13 // Description: |
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14 // e32\euser\maths\um_ln.cpp |
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15 // Natural log. |
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16 // |
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17 // |
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18 |
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19 #include "um_std.h" |
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20 |
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21 #if defined(__USE_VFP_MATH) && !defined(__CPU_HAS_VFP) |
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22 #error __USE_VFP_MATH was defined but not __CPU_HAS_VFP - impossible combination, check variant.mmh |
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23 #endif |
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24 |
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25 |
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26 #ifndef __USE_VFP_MATH |
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27 |
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28 LOCAL_D const TUint32 ArtanhCoeffs[] = |
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29 { |
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30 0x5C17F0BC,0xB8AA3B29,0x80010000, // polynomial approximation to (4/ln2)artanh(x) |
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31 0xD02489EE,0xF6384EE1,0x7FFF0000, // for |x| <= (sqr2-1)/(sqr2+1) |
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32 0x7008CA5F,0x93BB6287,0x7FFF0000, |
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33 0xE32D1D6B,0xD30BB16D,0x7FFE0000, |
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34 0x461D071E,0xA4257CE2,0x7FFE0000, |
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35 0xC3B0EC87,0x8650D459,0x7FFE0000, |
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36 0x53BEC0CD,0xE23137E3,0x7FFD0000, |
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37 0xC523F21B,0xDAF79221,0x7FFD0000 |
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38 }; |
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39 |
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40 LOCAL_D const TUint32 Ln2By2data[] = {0xD1CF79AC,0xB17217F7,0x7FFD0000}; // (ln2)/2 |
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41 LOCAL_D const TUint32 Sqr2data[] = {0xF9DE6484,0xB504F333,0x7FFF0000}; // sqr2 |
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42 LOCAL_D const TUint32 Sqr2Invdata[] = {0xF9DE6484,0xB504F333,0x7FFE0000}; // 1/sqr2 |
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43 LOCAL_D const TUint32 Onedata[] = {0x00000000,0x80000000,0x7FFF0000}; // 1.0 |
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44 |
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45 |
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46 |
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47 |
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48 EXPORT_C TInt Math::Ln(TReal& aTrg, const TReal& aSrc) |
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49 /** |
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50 Calculates the natural logarithm of a number. |
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51 |
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52 @param aTrg A reference containing the result. |
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53 @param aSrc The number whose natural logarithm is required. |
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54 |
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55 @return KErrNone if successful, otherwise another of |
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56 the system-wide error codes. |
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57 */ |
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58 { |
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59 // Calculate ln(aSrc) and write to aTrg |
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60 // Algorithm: |
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61 // Calculate log2(aSrc) and multiply by ln2 |
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62 // log2(aSrc)=log2(2^e.m) e=exponent of aSrc, m=mantissa 1<=m<2 |
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63 // log2(aSrc)=e+log2(m) |
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64 // If e=-1 (0.5<=aSrc<1), let x=aSrc else let x=mantissa(aSrc) |
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65 // If x>Sqr2, replace x with x/Sqr2 |
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66 // If x<Sqr2/2, replace x with x*Sqr2 |
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67 // Replace x with (x-1)/(x+1) |
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68 // Use polynomial to calculate artanh(x) for |x| <= (sqr2-1)/(sqr2+1) |
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69 // ( use identity ln(x) = 2artanh((x-1)/(x+1)) ) |
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70 |
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71 TRealX x; |
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72 const TRealX& Ln2By2=*(const TRealX*)Ln2By2data; |
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73 const TRealX& Sqr2=*(const TRealX*)Sqr2data; |
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74 const TRealX& Sqr2Inv=*(const TRealX*)Sqr2Invdata; |
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75 const TRealX& One=*(const TRealX*)Onedata; |
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76 |
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77 TInt r=x.Set(aSrc); |
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78 if (r==KErrNone) |
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79 { |
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80 if (x.iExp==0) |
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81 { |
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82 SetInfinite(aTrg,1); |
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83 return KErrOverflow; |
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84 } |
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85 if (x.iSign&1) |
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86 { |
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87 SetNaN(aTrg); |
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88 return KErrArgument; |
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89 } |
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90 TInt n=(x.iExp-0x7FFF)<<1; |
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91 x.iExp=0x7FFF; |
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92 if (n!=-2) |
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93 { |
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94 if (x>Sqr2) |
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95 { |
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96 x*=Sqr2Inv; |
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97 n++; |
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98 } |
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99 } |
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100 else |
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101 { |
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102 n=0; |
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103 x.iExp=0x7FFE; |
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104 if (x<Sqr2Inv) |
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105 { |
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106 x*=Sqr2; |
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107 n--; |
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108 } |
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109 } |
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110 x=(x-One)/(x+One); // ln(x)=2artanh((x-1)/(x+1)) |
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111 TRealX y; |
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112 PolyX(y,x*x,7,(const TRealX*)ArtanhCoeffs); |
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113 y*=x; |
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114 y+=TRealX(n); |
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115 y*=Ln2By2; |
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116 return y.GetTReal(aTrg); |
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117 } |
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118 if (r==KErrArgument || (r==KErrOverflow && (x.iSign&1))) |
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119 { |
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120 SetNaN(aTrg); |
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121 return KErrArgument; |
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122 } |
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123 SetInfinite(aTrg,0); |
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124 return KErrOverflow; |
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125 } |
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126 |
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127 #else // __USE_VFP_MATH |
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128 |
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129 // definitions come from RVCT math library |
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130 extern "C" TReal log(TReal); |
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131 |
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132 EXPORT_C TInt Math::Ln(TReal& aTrg, const TReal& aSrc) |
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133 { |
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134 aTrg = log(aSrc); |
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135 if (Math::IsFinite(aTrg)) |
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136 return KErrNone; |
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137 if (Math::IsInfinite(aTrg)) |
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138 return KErrOverflow; |
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139 SetNaN(aTrg); |
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140 return KErrArgument; |
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141 } |
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142 |
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143 #endif |