more cases

src/main/kotlin/ch/kleis/lcaplugin/ui/toolwindow/DisplayedNumber.kt

@@ -10,41 +10,48 @@ class DisplayedNumber(
 ) {
     private val isPositive: Boolean
     private val digits: List<Int>
-    private val exponent: Int
+    private val positionalExponent: Int
 
     init {
         fun prepareNonZero(v: Double): Pair<Int, List<Int>> {
             val w = abs(v)
-            val exponent = ceil(log10(w)).toInt()
-            val shift = nbSignificantDigits - exponent
-            val digits = ArrayList<Int>()
+            val positionalExponent = ceil(log10(w)).toInt()
+            val shift = nbSignificantDigits - positionalExponent
+            val reversedDigits = ArrayList<Int>()
             var u = floor(w * (10.0.pow(shift))).toInt()
             while (u > 0) {
-                digits.add(u.mod(10))
+                reversedDigits.add(u.mod(10))
                 u /= 10
             }
-
-            if (digits.take(nbSignificantDigits).all { it == 9 }) {
-                return exponent to listOf(1,) + listOf(0).replicate(nbSignificantDigits - 1).flatten()
+            val digits = reversedDigits.reversed()
+
+            if (digits.tail().take(nbSignificantDigits - 1).all { it == 9 }) {
+                val hd = digits[0]
+                if (hd == 9) {
+                    val zeros = listOf(0).replicate(nbSignificantDigits - 2).flatten()
+                    return positionalExponent to listOf(1, 0) + zeros
+                }
+                val zeros = listOf(0).replicate(nbSignificantDigits - 1).flatten()
+                return positionalExponent to listOf(hd + 1) + zeros
             }
 
-            return exponent to digits.reversed()
+            return positionalExponent to digits
         }
 
         if (value == 0.0) {
             isPositive = true
-            exponent = 1
+            positionalExponent = 1
             digits = IntRange(1, nbSignificantDigits).map { 0 }
         } else {
             val (e, d) = prepareNonZero(value)
             isPositive = value > 0.0
-            exponent = e
+            positionalExponent = e
             digits = d
         }
     }
 
     fun getExponent(): Int {
-        return exponent
+        return positionalExponent
     }
 
     fun getDigits(): List<Int> {
@@ -57,13 +64,13 @@ class DisplayedNumber(
     }
 
     private fun renderPowerOf10(): String {
-        return when (exponent) {
+        return when (positionalExponent) {
             -2 -> "0.01"
             -1 -> "0.1"
             0 -> "1"
             1 -> "10"
             2 -> "100"
-            else -> "1E$exponent"
+            else -> "1E$positionalExponent"
         }.let {
             if (isPositive) it else "-$it"
         }
@@ -79,17 +86,30 @@ class DisplayedNumber(
         }
 
         val midpoint = when {
-            exponent < 0 -> 1
-            exponent <= nbSignificantDigits -> exponent
+            positionalExponent <= -nbSignificantDigits + 1 -> 1
+            -nbSignificantDigits + 1 < positionalExponent
+                && positionalExponent < nbSignificantDigits -> positionalExponent
+
             else -> nbSignificantDigits
         }
-        val displayedExponent = exponent - midpoint
+        val displayedExponent = when {
+            -nbSignificantDigits + 1 < positionalExponent
+                && positionalExponent < nbSignificantDigits -> 0
 
-        val head = digits.subList(0, midpoint).joinToString("")
-            .ifEmpty { "0" }
-        val tail = digits.subList(midpoint, nbSignificantDigits)
-            .dropLastWhile { it == 0 }
-            .joinToString("")
+            else -> positionalExponent - midpoint
+        }
+
+        val head = when {
+            midpoint <= 0 -> emptyList()
+            else -> digits.subList(0, midpoint)
+        }.joinToString("").ifEmpty { "0" }
+        val tail = when {
+            midpoint <= 0 -> {
+                val prefix = listOf(0).replicate(-midpoint).flatten()
+                prefix + digits.take(nbSignificantDigits)
+            }
+            else -> digits.subList(midpoint, nbSignificantDigits)
+        }.dropLastWhile { it == 0 }.joinToString("")
 
         val sign = if (isPositive) "" else "-"
         val e = if (displayedExponent == 0) "" else "E$displayedExponent"

src/test/kotlin/ch/kleis/lcaplugin/ui/toolwindow/DisplayedNumberTest.kt

@@ -37,11 +37,19 @@ class DisplayedNumberTest {
             99.9 to "100",
             999.0 to "1E3",
 
-            0.0123 to "1.23E-2",
+            0.003999 to "4E-3",
+            0.04999 to "0.05",
+            0.5999 to "0.6",
+            6.999 to "7",
+            79.90 to "80",
+            899.9 to "900",
+            999.0 to "1E3",
+
+            0.00123 to "1.23E-3",
+            0.0123 to "0.0123",
             0.123 to "0.123",
             1.2345 to "1.23",
             12345.123 to "123E2",
-            0.00123 to "1.23E-3",
 
             -0.0 to "0",
             -0.0001 to "-1E-4",
@@ -52,7 +60,7 @@ class DisplayedNumberTest {
             -100.0 to "-100",
             -1000.0 to "-1E3",
 
-            -0.0123 to "-1.23E-2",
+            -0.0123 to "-0.0123",
             -0.123 to "-0.123",
             -1.2345 to "-1.23",
             -12345.123 to "-123E2",