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comparison app/src/main/java/com/bartsent/simpleresizer/lib/LanczosKernel.kt @ 8:6ae738b8a814 memo

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Memoize. Only modest improvement results.
author David Barts <n5jrn@me.com>
date Wed, 17 Feb 2021 07:43:50 -0800
parents e8059b166de1
children 678adef4774f
comparison
equal deleted inserted replaced
6:e8059b166de1 8:6ae738b8a814
4 import kotlin.math.abs 4 import kotlin.math.abs
5 import kotlin.math.sin 5 import kotlin.math.sin
6 6
7 object LanczosKernel: ScalingKernel { 7 object LanczosKernel: ScalingKernel {
8 override val size = 3.0 8 override val size = 3.0
9 private val memory = HashMap<Double, Double>()
10 init {
11 memory.put(0.0, 1.0)
12 }
9 13
10 private fun sinc(x: Double): Double { 14 private fun sinc(x: Double): Double {
11 if (x == 0.0) 15 val remembered = memory.get(x)
12 return 1.0 16 if (remembered != null)
17 return remembered
13 val pix = PI * x 18 val pix = PI * x
14 return sin(pix) / pix 19 val calculated = sin(pix) / pix
20 memory.put(x, calculated)
21 return calculated
15 } 22 }
16 23
17 override fun weight(x: Double): Double = 24 override fun weight(x: Double): Double =
18 if (abs(x) < size) sinc(x) * sinc(x/size) else 0.0 25 if (abs(x) < size) sinc(x) * sinc(x/size) else 0.0
19 } 26 }