ref: 8d4ed75503a050a4202520ea90bea5a79fa247e8
parent: 6fdeebb610e41db8b9e57fe2ea66b379ff6b5078
author: Olav Sørensen <olav.sorensen@live.no>
date: Tue May 20 16:45:00 EDT 2025
Update ft2_tables.c
--- a/src/ft2_tables.c
+++ b/src/ft2_tables.c
@@ -79,6 +79,9 @@
53, 50, 47, 45, 42, 40, 37, 35, 33, 31, 30, 28
};
+// Formula:
+// for (i = 0 to 1935) x = (1936 - i) * 4
+//
const uint16_t linearPeriodLUT[1936] = // bit-exact to FT2 table
{7744, 7740, 7736, 7732, 7728, 7724, 7720, 7716, 7712, 7708, 7704, 7700, 7696, 7692, 7688, 7684,
@@ -204,6 +207,9 @@
64, 60, 56, 52, 48, 44, 40, 36, 32, 28, 24, 20, 16, 12, 8, 4
};
+// The original formula is over-engineered and buggy. A simpler (and more accurate) formula would be:
+// for (i = 0 to 1935) x = round[(1712*4*16) / 2^((368+i) / (12*16))]
+//
const uint16_t amigaPeriodLUT[1936] = // bit-exact to FT2 table
{29024, 28912, 28800, 28704, 28608, 28496, 28384, 28288, 28192, 28096, 28000, 27888, 27776, 27680, 27584, 27488,
--
⑨