Created
June 21, 2020 17:53
-
-
Save nicolasnoble/4a2a73fbc04fb8c25c1c95112ae34bca to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| class DiscreteCos { | |
| public: | |
| DiscreteCos() { generate(); } | |
| static const unsigned int DC_2PI = 2048; | |
| static const unsigned int DC_PI = 1024; | |
| static const unsigned int DC_PI2 = 512; | |
| int32_t cos(unsigned int t) { | |
| t %= DC_2PI; | |
| int32_t r; | |
| if (t < DC_PI2) { | |
| r = m_cosTable[t]; | |
| } else if (t < DC_PI) { | |
| r = -m_cosTable[DC_PI - 1 - t]; | |
| } else if (t < (DC_PI + DC_PI2)) { | |
| r = -m_cosTable[t - DC_PI]; | |
| } else { | |
| r = m_cosTable[DC_2PI - 1 - t]; | |
| } | |
| return r; | |
| } | |
| // sin(x) = cos(x - pi / 2) | |
| int32_t sin(unsigned int t) { | |
| t %= DC_2PI; | |
| if (t < DC_PI2) | |
| return cos(t + DC_2PI - DC_PI2); | |
| return cos(t - DC_PI2); | |
| } | |
| private: | |
| int32_t m_cosTable[512]; | |
| // f(n) = cos(n * 2pi / 2048) | |
| // f(n) = 2 * f(1) * f(n - 1) - f(n - 2) | |
| void generate() { | |
| m_cosTable[0] = 16777216; // 2^24 * cos(0 * 2pi / 2048) | |
| int64_t C = m_cosTable[1] = 16777137; // 2^24 * cos(1 * 2pi / 2048) = C = f(1); | |
| for (int i = 2; i < 512; i++) | |
| m_cosTable[i] = ((C * m_cosTable[i - 1]) >> 23) - m_cosTable[i - 2]; | |
| m_cosTable[511] = 0; | |
| } | |
| }; | |
| DiscreteCos dc; |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment