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

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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
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39
audio/internal/convert/resampling.go
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@ -29,42 +29,41 @@ func init() {
}
}
func fastCos(x float64) float64 {
func fastCos01(x float64) float64 {
if x < 0 {
x = -x
}
x /= 2 * math.Pi
if 1 < x {
_, x = math.Modf(x)
i := int(4 * float64(len(cosTable)) * x)
if 4*len(cosTable) < i {
i %= 4 * len(cosTable)
}
sign := 1
switch {
case x < 0.25:
case x < 0.5:
x = 0.5 - x
case i < len(cosTable):
case i < len(cosTable)*2:
i = len(cosTable)*2 - i
sign = -1
case x < 0.75:
x -= 0.5
case i < len(cosTable)*3:
i -= len(cosTable) * 2
sign = -1
default:
x = 1 - x
i = len(cosTable)*4 - i
}
idx := int(4 * x * float64(len(cosTable)))
if idx == len(cosTable) {
if i == len(cosTable) {
return 0
}
return float64(sign) * cosTable[idx]
return float64(sign) * cosTable[i]
}
func fastSin(x float64) float64 {
return fastCos(x - math.Pi/2)
func fastSin01(x float64) float64 {
return fastCos01(x - 0.25)
}
func sinc(x float64) float64 {
func sinc01(x float64) float64 {
if math.Abs(x) < 1e-8 {
return 1
}
return fastSin(x) / x
return fastSin01(x) / (x * 2 * math.Pi)
}
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) {
windowSize := 8.0
windowSize := 4.0
tInSrc := float64(t) * float64(r.from) / float64(r.to)
startN := int64(tInSrc - windowSize)
if startN < 0 {
@ -184,8 +183,8 @@ func (r *Resampling) at(t int64) (float64, float64, error) {
return 0, 0, err
}
d := tInSrc - float64(n)
w := 0.5 + 0.5*fastCos(2*math.Pi*d/(windowSize*2+1))
s := sinc(math.Pi*d) * w
w := 0.5 + 0.5*fastCos01(d/(windowSize*2+1))
s := sinc01(d/2) * w
lv += srcL * s
rv += srcR * s
}