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Wraps log_sin in an access function to enshrine sign and mask rules; switches both functions to non-math.h clashing names.

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Thomas Harte 2020-04-17 23:22:42 -04:00
parent 6f7c8b35c5
commit 4a295cd95e
1 changed files with 60 additions and 44 deletions
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104
Components/OPL2/Implementation/Tables.h
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@ -21,55 +21,71 @@ namespace OPL {
*/
/// Defines the first quadrant of 1024-unit negative log to the base two of sine (that conveniently misses sin(0)).
///
/// Expected branchless usage for a full 1024 unit output:
///
/// constexpr int multiplier[] = { 1, -1 };
/// constexpr int mask[] = { 0, 255 };
///
/// value = exp( log_sin[angle & 255] ^ mask[(angle >> 8) & 1]) * multitplier[(angle >> 9) & 1]
///
/// ... where exp(x) = 2 ^ -x / 256
constexpr int16_t log_sin[] = {
2137, 1731, 1543, 1419, 1326, 1252, 1190, 1137,
1091, 1050, 1013, 979, 949, 920, 894, 869,
846, 825, 804, 785, 767, 749, 732, 717,
701, 687, 672, 659, 646, 633, 621, 609,
598, 587, 576, 566, 556, 546, 536, 527,
518, 509, 501, 492, 484, 476, 468, 461,
453, 446, 439, 432, 425, 418, 411, 405,
399, 392, 386, 380, 375, 369, 363, 358,
352, 347, 341, 336, 331, 326, 321, 316,
311, 307, 302, 297, 293, 289, 284, 280,
276, 271, 267, 263, 259, 255, 251, 248,
244, 240, 236, 233, 229, 226, 222, 219,
215, 212, 209, 205, 202, 199, 196, 193,
190, 187, 184, 181, 178, 175, 172, 169,
167, 164, 161, 159, 156, 153, 151, 148,
146, 143, 141, 138, 136, 134, 131, 129,
127, 125, 122, 120, 118, 116, 114, 112,
110, 108, 106, 104, 102, 100, 98, 96,
94, 92, 91, 89, 87, 85, 83, 82,
80, 78, 77, 75, 74, 72, 70, 69,
67, 66, 64, 63, 62, 60, 59, 57,
56, 55, 53, 52, 51, 49, 48, 47,
46, 45, 43, 42, 41, 40, 39, 38,
37, 36, 35, 34, 33, 32, 31, 30,
29, 28, 27, 26, 25, 24, 23, 23,
22, 21, 20, 20, 19, 18, 17, 17,
16, 15, 15, 14, 13, 13, 12, 12,
11, 10, 10, 9, 9, 8, 8, 7,
7, 7, 6, 6, 5, 5, 5, 4,
4, 4, 3, 3, 3, 2, 2, 2,
2, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0
struct LogSin {
int logsin;
int sign;
};
/*!
@returns Negative log sin of x, assuming a 1024-unit circle.
*/
constexpr LogSin negative_log_sin(int x) {
/// Defines the first quadrant of 1024-unit negative log to the base two of sine (that conveniently misses sin(0)).
///
/// Expected branchless usage for a full 1024 unit output:
///
/// constexpr int multiplier[] = { 1, -1 };
/// constexpr int mask[] = { 0, 255 };
///
/// value = exp( log_sin[angle & 255] ^ mask[(angle >> 8) & 1]) * multitplier[(angle >> 9) & 1]
///
/// ... where exp(x) = 2 ^ -x / 256
constexpr int16_t log_sin[] = {
2137, 1731, 1543, 1419, 1326, 1252, 1190, 1137,
1091, 1050, 1013, 979, 949, 920, 894, 869,
846, 825, 804, 785, 767, 749, 732, 717,
701, 687, 672, 659, 646, 633, 621, 609,
598, 587, 576, 566, 556, 546, 536, 527,
518, 509, 501, 492, 484, 476, 468, 461,
453, 446, 439, 432, 425, 418, 411, 405,
399, 392, 386, 380, 375, 369, 363, 358,
352, 347, 341, 336, 331, 326, 321, 316,
311, 307, 302, 297, 293, 289, 284, 280,
276, 271, 267, 263, 259, 255, 251, 248,
244, 240, 236, 233, 229, 226, 222, 219,
215, 212, 209, 205, 202, 199, 196, 193,
190, 187, 184, 181, 178, 175, 172, 169,
167, 164, 161, 159, 156, 153, 151, 148,
146, 143, 141, 138, 136, 134, 131, 129,
127, 125, 122, 120, 118, 116, 114, 112,
110, 108, 106, 104, 102, 100, 98, 96,
94, 92, 91, 89, 87, 85, 83, 82,
80, 78, 77, 75, 74, 72, 70, 69,
67, 66, 64, 63, 62, 60, 59, 57,
56, 55, 53, 52, 51, 49, 48, 47,
46, 45, 43, 42, 41, 40, 39, 38,
37, 36, 35, 34, 33, 32, 31, 30,
29, 28, 27, 26, 25, 24, 23, 23,
22, 21, 20, 20, 19, 18, 17, 17,
16, 15, 15, 14, 13, 13, 12, 12,
11, 10, 10, 9, 9, 8, 8, 7,
7, 7, 6, 6, 5, 5, 5, 4,
4, 4, 3, 3, 3, 2, 2, 2,
2, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0
};
constexpr int16_t sign[] = { 1, -1 };
constexpr int16_t mask[] = { 0, 255 };
return {
.logsin = log_sin[x & 255] ^ mask[(x >> 8) & 1],
.sign = sign[(x >> 9) & 1]
};
}
/*!
@returns 2 ^ -x/256 in 0.10 fixed-point form.
*/
constexpr int exp(int x) {
constexpr int power_two(int x) {
/// A derivative of the exponent table in a real OPL2; mapped_exp[x] = (source[c ^ 0xff] << 1) | 0x800.
///
/// The ahead-of-time transformation represents fixed work the OPL2 does when reading its table