kai/pounder_test
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

atan2: clarify sharing bits between atan argument and constant factors

Browse Source
This commit is contained in:
Matt Huszagh 2020-12-17 09:31:38 -08:00
parent 5717991ada
commit cb38c3e3bd
1 changed files with 12 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
dsp/src/trig.rs
View File

@ -47,16 +47,21 @@ pub fn atan2(y: i32, x: i32) -> i32 {
return 0; return 0;
} }
let ratio = (min << 15) / max; // We need to share the 31 available non-sign bits between the
// atan argument and constant factors used in the atan
// approximation. Sharing the bits roughly equally between them
// gives good accuracy.
const ATAN_ARGUMENT_BITS: usize = 15;
let ratio = (min << ATAN_ARGUMENT_BITS) / max;
let mut angle = { let mut angle = {
const K1: i32 = const K1: i32 = ((1. / 4. + 0.285 / PI)
((1_f64 / 4_f64 + 0.285_f64 / PI) * (1 << 16) as f64) as i32; * (1 << (31 - ATAN_ARGUMENT_BITS)) as f64)
const K2: i32 = ((0.285_f64 / PI) * (1 << 16) as f64) as i32; as i32;
const K2: i32 =
((0.285 / PI) * (1 << (31 - ATAN_ARGUMENT_BITS)) as f64) as i32;
let ratio_squared = shift_round(ratio * ratio, 15); ratio * K1 - K2 * shift_round(ratio * ratio, ATAN_ARGUMENT_BITS)
ratio * K1 - K2 * ratio_squared
}; };
if uy > ux { if uy > ux {