refactor: add channel hash function

app/src/androidTest/java/com/geeksville/mesh/ChannelTest.kt

@@ -4,6 +4,7 @@ import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.geeksville.mesh.model.Channel
 import com.geeksville.mesh.model.URL_PREFIX
 import com.geeksville.mesh.model.getChannelUrl
+import com.geeksville.mesh.model.numChannels
 import com.geeksville.mesh.model.toChannelSet
 import org.junit.Assert
 import org.junit.Test
@@ -23,6 +24,20 @@ class ChannelTest {
         Assert.assertEquals(channelUrl.toChannelSet(), ch)
     }
 
+    @Test
+    fun channelHashGood() {
+        val ch = Channel.default
+
+        Assert.assertEquals(8, ch.hash)
+    }
+
+    @Test
+    fun numChannelsGood() {
+        val ch = Channel.default
+
+        Assert.assertEquals(104, ch.loraConfig.numChannels)
+    }
+
     @Test
     fun channelNumGood() {
         val ch = Channel.default

app/src/main/java/com/geeksville/mesh/model/Channel.kt

@@ -89,24 +89,13 @@ data class Channel(
         }
 
     /**
-     * hash a string into an integer using the djb2 algorithm by Dan Bernstein
-     * http://www.cse.yorku.ca/~oz/hash.html
+     * Given a channel name and psk, return the (0 to 255) hash for that channel
      */
-    val hash: UInt // using UInt instead of Long to match RadioInterface.cpp results
-        get() {
-            var hash: UInt = 5381u
-            for (c in name) {
-                hash += (hash shl 5) + c.code.toUInt()
-                print("$c ${c.code} $hash ")
-            }
-            return hash
-        }
+    val hash: Int get() = xorHash(name.toByteArray()) xor xorHash(psk.toByteArray())
 
-    val channelNum: Int
-        get() = if (loraConfig.channelNum != 0) loraConfig.channelNum
-        else (hash % RegionInfo.numChannels(loraConfig).toUInt()).toInt() + 1
+    val channelNum: Int get() = loraConfig.channelNum(name)
 
-    val radioFreq: Float get() = RegionInfo.radioFreq(loraConfig, channelNum)
+    val radioFreq: Float get() = loraConfig.radioFreq(channelNum)
 
     override fun equals(other: Any?): Boolean = (other is Channel)
             && psk.toByteArray() contentEquals other.psk.toByteArray()

app/src/main/java/com/geeksville/mesh/model/ChannelOption.kt

@@ -5,9 +5,29 @@ import com.geeksville.mesh.ConfigProtos.Config.LoRaConfig.ModemPreset
 import com.geeksville.mesh.ConfigProtos.Config.LoRaConfig.RegionCode
 import com.geeksville.mesh.R
 
-fun LoRaConfig.bandwidth() = if (usePreset) {
+/**
+ * hash a string into an integer using the djb2 algorithm by Dan Bernstein
+ * http://www.cse.yorku.ca/~oz/hash.html
+ */
+private fun hash(name: String): UInt { // using UInt instead of Long to match RadioInterface.cpp results
+    var hash: UInt = 5381u
+    for (c in name) {
+        hash += (hash shl 5) + c.code.toUInt()
+    }
+    return hash
+}
+
+private val ModemPreset.bandwidth: Float
+    get() {
+        for (option in ChannelOption.entries) {
+            if (option.modemPreset == this) return option.bandwidth
+        }
+        return 0f
+    }
+
+private fun LoRaConfig.bandwidth() = if (usePreset) {
     val wideLora = region == RegionCode.LORA_24
-    ChannelOption.bandwidth(modemPreset) * if (wideLora) 3.25f else 1f
+    modemPreset.bandwidth * if (wideLora) 3.25f else 1f
 } else when (bandwidth) {
     31 -> .03125f
     62 -> .0625f
@@ -18,6 +38,28 @@ fun LoRaConfig.bandwidth() = if (usePreset) {
     else -> bandwidth / 1000f
 }
 
+val LoRaConfig.numChannels: Int get() {
+    for (option in RegionInfo.entries) {
+        if (option.regionCode == region)
+            return ((option.freqEnd - option.freqStart) / bandwidth()).toInt()
+    }
+    return 0
+}
+
+internal fun LoRaConfig.channelNum(primaryName: String): Int {
+    return if (channelNum != 0) channelNum
+    else (hash(primaryName) % numChannels.toUInt()).toInt() + 1
+}
+
+internal fun LoRaConfig.radioFreq(channelNum: Int): Float {
+    if (overrideFrequency != 0f) return overrideFrequency + frequencyOffset
+    for (option in RegionInfo.entries) {
+        if (option.regionCode == region)
+            return (option.freqStart + bandwidth() / 2) + (channelNum - 1) * bandwidth()
+    }
+    return 0f
+}
+
 enum class RegionInfo(
     val regionCode: RegionCode,
     val freqStart: Float,
@@ -38,26 +80,8 @@ enum class RegionInfo(
     UA_433(RegionCode.UA_433, 433.0f, 434.7f),
     UA_868(RegionCode.UA_868, 868.0f, 868.6f),
     LORA_24(RegionCode.LORA_24, 2400.0f, 2483.5f),
-    UNSET(RegionCode.UNSET, 902.0f, 928.0f);
-
-    companion object {
-        fun numChannels(loraConfig: LoRaConfig): Int {
-            for (option in values()) {
-                if (option.regionCode == loraConfig.region)
-                    return ((option.freqEnd - option.freqStart) / loraConfig.bandwidth()).toInt()
-            }
-            return 0
-        }
-
-        fun radioFreq(loraConfig: LoRaConfig, channelNum: Int): Float = with(loraConfig) {
-            if (overrideFrequency != 0f) return overrideFrequency + frequencyOffset
-            for (option in values()) {
-                if (option.regionCode == region)
-                    return (option.freqStart + bandwidth() / 2) + (channelNum - 1) * bandwidth()
-            }
-            return 0f
-        }
-    }
+    UNSET(RegionCode.UNSET, 902.0f, 928.0f),
+    ;
 }
 
 enum class ChannelOption(
@@ -74,13 +98,4 @@ enum class ChannelOption(
     LONG_SLOW(ModemPreset.LONG_SLOW, R.string.modem_config_slow_long, .125f),
     VERY_LONG_SLOW(ModemPreset.VERY_LONG_SLOW, R.string.modem_config_very_long, .0625f),
     ;
-
-    companion object {
-        fun bandwidth(modemPreset: ModemPreset?): Float {
-            for (option in values()) {
-                if (option.modemPreset == modemPreset) return option.bandwidth
-            }
-            return 0f
-        }
-    }
 }

app/src/main/java/com/geeksville/mesh/ui/components/config/LoRaConfigItemList.kt

@@ -16,7 +16,7 @@ import com.geeksville.mesh.ChannelProtos.ChannelSettings
 import com.geeksville.mesh.ConfigProtos.Config.LoRaConfig
 import com.geeksville.mesh.copy
 import com.geeksville.mesh.model.Channel
-import com.geeksville.mesh.model.RegionInfo
+import com.geeksville.mesh.model.numChannels
 import com.geeksville.mesh.ui.components.DropDownPreference
 import com.geeksville.mesh.ui.components.EditListPreference
 import com.geeksville.mesh.ui.components.EditTextPreference
@@ -136,7 +136,7 @@ fun LoRaConfigItemList(
                 keyboardActions = KeyboardActions(onDone = { focusManager.clearFocus() }),
                 onFocusChanged = { isFocused = it.isFocused },
                 onValueChanged = {
-                    if (it <= RegionInfo.numChannels(loraInput)) // max numChannels
+                    if (it <= loraInput.numChannels) // total num of LoRa channels
                         loraInput = loraInput.copy { channelNum = it }
                 })
         }