mth/ebiten
1
0
Fork 0
mirror of https://github.com/hajimehoshi/ebiten.git synced 2025-01-12 20:18:59 +01:00
Code Issues Packages Projects Releases Wiki Activity

audio/internal/convert: Much faster sine/cosine functions

Browse Source
This commit is contained in:
Hajime Hoshi 2018-01-06 00:15:07 +09:00
parent 005d18ceff
commit ab70f6fc58
1 changed files with 19 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
audio/internal/convert/resampling.go
View File

@ -29,42 +29,41 @@ func init() {
} }
} }
func fastCos(x float64) float64 { func fastCos01(x float64) float64 {
if x < 0 { if x < 0 {
x = -x x = -x
} }
x /= 2 * math.Pi i := int(4 * float64(len(cosTable)) * x)
if 1 < x { if 4*len(cosTable) < i {
_, x = math.Modf(x) i %= 4 * len(cosTable)
} }
sign := 1 sign := 1
switch { switch {
case x < 0.25: case i < len(cosTable):
case x < 0.5: case i < len(cosTable)*2:
x = 0.5 - x i = len(cosTable)*2 - i
sign = -1 sign = -1
case x < 0.75: case i < len(cosTable)*3:
x -= 0.5 i -= len(cosTable) * 2
sign = -1 sign = -1
default: default:
x = 1 - x i = len(cosTable)*4 - i
} }
idx := int(4 * x * float64(len(cosTable))) if i == len(cosTable) {
if idx == len(cosTable) {
return 0 return 0
} }
return float64(sign) * cosTable[idx] return float64(sign) * cosTable[i]
} }
func fastSin(x float64) float64 { func fastSin01(x float64) float64 {
return fastCos(x - math.Pi/2) return fastCos01(x - 0.25)
} }
func sinc(x float64) float64 { func sinc01(x float64) float64 {
if math.Abs(x) < 1e-8 { if math.Abs(x) < 1e-8 {
return 1 return 1
} }
return fastSin(x) / x return fastSin01(x) / (x * 2 * math.Pi)
} }
type Resampling struct { type Resampling struct {
@ -163,7 +162,7 @@ func (r *Resampling) src(i int64) (float64, float64, error) {
} }
func (r *Resampling) at(t int64) (float64, float64, error) { func (r *Resampling) at(t int64) (float64, float64, error) {
windowSize := 8.0 windowSize := 4.0
tInSrc := float64(t) * float64(r.from) / float64(r.to) tInSrc := float64(t) * float64(r.from) / float64(r.to)
startN := int64(tInSrc - windowSize) startN := int64(tInSrc - windowSize)
if startN < 0 { if startN < 0 {
@ -184,8 +183,8 @@ func (r *Resampling) at(t int64) (float64, float64, error) {
return 0, 0, err return 0, 0, err
} }
d := tInSrc - float64(n) d := tInSrc - float64(n)
w := 0.5 + 0.5*fastCos(2*math.Pi*d/(windowSize*2+1)) w := 0.5 + 0.5*fastCos01(d/(windowSize*2+1))
s := sinc(math.Pi*d) * w s := sinc01(d/2) * w
lv += srcL * s lv += srcL * s
rv += srcR * s rv += srcR * s
} }