* @returns Base 2 logarithm of the value. * This is fast, inline and quite accurate algorithm. * Accuracy: ~1.e-5 * Speed: ~3x over logf() * Source: https://code.google.com/archive/p/fastapprox/ * Description: http://www.machinedlearnings.com/2011/06/fast-approximate-logarithm-exponential.html */
| 60 | * Description: http://www.machinedlearnings.com/2011/06/fast-approximate-logarithm-exponential.html |
| 61 | */ |
| 62 | static inline float FastLog2f(float value) noexcept { |
| 63 | Y_ASSERT(LogInputCheck(value)); |
| 64 | union { |
| 65 | float f; |
| 66 | ui32 i; |
| 67 | } vx = {value}; |
| 68 | union { |
| 69 | ui32 i; |
| 70 | float f; |
| 71 | } mx = {(vx.i & 0x007FFFFF) | 0x3f000000}; |
| 72 | float y = vx.i; |
| 73 | y *= 1.1920928955078125e-7f; |
| 74 | |
| 75 | return y - 124.22551499f - 1.498030302f * mx.f - 1.72587999f / (0.3520887068f + mx.f); |
| 76 | } |
| 77 | |
| 78 | /** |
| 79 | * @returns Base e logarithm of the value. |
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