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Use separate function for calculating input diff when Base64 decoding #237

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Merged
05nelsonm merged 1 commit into from
Dec 14, 2025
Merged

Use separate function for calculating input diff when Base64 decoding #237

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71 changes: 37 additions & 34 deletions library/base64/src/commonMain/kotlin/io/matthewnelson/encoding/base64/Base64.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -422,40 +422,7 @@ public class Base64: EncoderDecoder<Base64.Config> {

override fun consumeProtected(input: Char) {
val code = input.code

val ge0: Byte = if (code >= '0'.code) 1 else 0
val le9: Byte = if (code <= '9'.code) 1 else 0
val geA: Byte = if (code >= 'A'.code) 1 else 0
val leZ: Byte = if (code <= 'Z'.code) 1 else 0
val gea: Byte = if (code >= 'a'.code) 1 else 0
val lez: Byte = if (code <= 'z'.code) 1 else 0
val eqPlu: Byte = if (code == '+'.code) 1 else 0
val eqMin: Byte = if (code == '-'.code) 1 else 0
val eqSla: Byte = if (code == '/'.code) 1 else 0
val eqUSc: Byte = if (code == '_'.code) 1 else 0

var diff = 0

// char ASCII value
// 0 48 52
// 9 57 61 (ASCII + 4)
diff += if (ge0 + le9 == 2) 4 else 0

// char ASCII value
// A 65 0
// Z 90 25 (ASCII - 65)
diff += if (geA + leZ == 2) -65 else 0

// char ASCII value
// a 97 26
// z 122 51 (ASCII - 71)
diff += if (gea + lez == 2) -71 else 0

val h = 62 - code
val k = 63 - code
diff += if (eqPlu + eqMin == 1) h else 0
diff += if (eqSla + eqUSc == 1) k else 0

val diff = code.decodeDiff()
if (diff == 0) {
throw MalformedEncodingException("Char[$input] is not a valid $NAME character")
}
Expand Down Expand Up @@ -504,6 +471,42 @@ public class Base64: EncoderDecoder<Base64.Config> {
// "Should" never make it here
error("Illegal configuration >> count[$count]")
}

private fun Int.decodeDiff(): Int {
val ge0: Byte = if (this >= '0'.code) 1 else 0
val le9: Byte = if (this <= '9'.code) 1 else 0
val geA: Byte = if (this >= 'A'.code) 1 else 0
val leZ: Byte = if (this <= 'Z'.code) 1 else 0
val gea: Byte = if (this >= 'a'.code) 1 else 0
val lez: Byte = if (this <= 'z'.code) 1 else 0
val eqPlu: Byte = if (this == '+'.code) 1 else 0
val eqMin: Byte = if (this == '-'.code) 1 else 0
val eqSla: Byte = if (this == '/'.code) 1 else 0
val eqUSc: Byte = if (this == '_'.code) 1 else 0

var diff = 0

// char ASCII value
// 0 48 52
// 9 57 61 (ASCII + 4)
diff += if (ge0 + le9 == 2) 4 else 0

// char ASCII value
// A 65 0
// Z 90 25 (ASCII - 65)
diff += if (geA + leZ == 2) -65 else 0

// char ASCII value
// a 97 26
// z 122 51 (ASCII - 71)
diff += if (gea + lez == 2) -71 else 0

val h = 62 - this
val k = 63 - this
diff += if (eqPlu + eqMin == 1) h else 0
diff += if (eqSla + eqUSc == 1) k else 0
return diff
}
}

private abstract inner class EncoderFeed(out: Encoder.OutFeed): Encoder<Config>.Feed(_out = out) {
Expand Down