From cd3f7897ff44deea673686dda9dc0758417e3d7e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gre=CC=81gory=20Lureau?= <gregory.lureau@sumup.com>
Date: Mon, 10 Jun 2024 19:00:44 +0200
Subject: [PATCH] Improve performances of BigDecimal.numberOfDecimalDigits().

---
 .../kotlin/bignum/decimal/BigDecimal.kt       | 14 ++++++++++++-
 .../bignum/decimal/BigDecimalRoundingTests.kt | 21 ++++++++++---------
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimal.kt b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimal.kt
index add0f441..2e803a7f 100644
--- a/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimal.kt
+++ b/bignum/src/commonMain/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimal.kt
@@ -1484,6 +1484,7 @@ class BigDecimal private constructor(
      * 12.345 will return 5
      * 0.001 will return 4
      * 123000 will return 6
+     * 0.010000 will return 3 (trailing zeros are not counted)
      */
     override fun numberOfDecimalDigits(): Long {
         val numberOfDigits = when {
@@ -1491,7 +1492,18 @@ class BigDecimal private constructor(
             exponent > 0 && exponent > precision -> exponent + 1 // Significand is already 10^1 when exponent is > 0
             exponent > 0 && exponent == precision -> precision + 1 // Same as above
             exponent < 0 -> exponent.absoluteValue + precision
-            exponent == 0L -> removeTrailingZeroes(this).precision
+            exponent == 0L -> {
+                var s = significand
+                if (s.isZero()) return 1L
+                var zeroCount = -1L
+                do {
+                    val res = s.divrem(BigInteger.TEN)
+                    s = res.quotient
+                    zeroCount++
+                } while (res.remainder.isZero())
+                precision - zeroCount
+            }
+
             else -> throw RuntimeException("Invalid case when getting number of decimal digits")
         }
         return numberOfDigits
diff --git a/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimalRoundingTests.kt b/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimalRoundingTests.kt
index 6ad2b039..64526df7 100644
--- a/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimalRoundingTests.kt
+++ b/bignum/src/commonTest/kotlin/com/ionspin/kotlin/bignum/decimal/BigDecimalRoundingTests.kt
@@ -31,17 +31,18 @@ class BigDecimalRoundingTests {
 
     @Test
     fun testNumberOfDigits() {
-        val a = BigDecimal.fromIntWithExponent(123, 3)
-        val b = BigDecimal.fromIntWithExponent(1, -3)
-        val c = BigDecimal.fromIntWithExponent(12345, 3)
-        val d = BigDecimal.fromIntAsSignificand(10000)
-        assertTrue {
-            a.numberOfDecimalDigits() == 4L &&
-                    b.numberOfDecimalDigits() == 4L &&
-                    c.numberOfDecimalDigits() == 5L &&
-                    d.numberOfDecimalDigits() == 1L
+        assertEquals(4, BigDecimal.parseString("1230").numberOfDecimalDigits())
+        assertEquals(4, BigDecimal.parseString("0.001").numberOfDecimalDigits())
+        assertEquals(5, BigDecimal.parseString("1234.5").numberOfDecimalDigits())
+        assertEquals(1, BigDecimal.parseString("1.0000").numberOfDecimalDigits())
+        assertEquals(5, BigDecimal.parseString("1.0001000").numberOfDecimalDigits())
+        assertEquals(6, BigDecimal.parseString("10.0001000").numberOfDecimalDigits())
+        assertEquals(1, BigDecimal.parseString("0").numberOfDecimalDigits())
+        assertEquals(1, BigDecimal.parseString("0.0").numberOfDecimalDigits())
+        assertEquals(1, BigDecimal.parseString("00.00").numberOfDecimalDigits())
+        assertEquals(1, BigDecimal.parseString("1").numberOfDecimalDigits())
+        assertEquals(2, BigDecimal.parseString("10").numberOfDecimalDigits())
         }
-    }
 
     @Test
     fun testRoundSignificand() {