From 935b3f0e11e9e8684fa92a0c170a7cf4cbdb83b2 Mon Sep 17 00:00:00 2001
From: Egor Andreevich <egor@squareup.com>
Date: Thu, 14 Nov 2024 12:26:22 -0500
Subject: [PATCH] Improve algorithm to count digits in Long (#1548)

---
 .../commonMain/kotlin/okio/internal/Buffer.kt | 86 +++++++------------
 .../kotlin/okio/CommonBufferedSinkTest.kt     | 36 ++++++++
 2 files changed, 65 insertions(+), 57 deletions(-)

diff --git a/okio/src/commonMain/kotlin/okio/internal/Buffer.kt b/okio/src/commonMain/kotlin/okio/internal/Buffer.kt
index 2270fc1dcc..13194403ee 100644
--- a/okio/src/commonMain/kotlin/okio/internal/Buffer.kt
+++ b/okio/src/commonMain/kotlin/okio/internal/Buffer.kt
@@ -461,63 +461,7 @@ internal inline fun Buffer.commonWriteDecimalLong(v: Long): Buffer {
     negative = true
   }
 
-  // Binary search for character width which favors matching lower numbers.
-  var width =
-    if (v < 100000000L) {
-      if (v < 10000L) {
-        if (v < 100L) {
-          if (v < 10L) {
-            1
-          } else {
-            2
-          }
-        } else if (v < 1000L) {
-          3
-        } else {
-          4
-        }
-      } else if (v < 1000000L) {
-        if (v < 100000L) {
-          5
-        } else {
-          6
-        }
-      } else if (v < 10000000L) {
-        7
-      } else {
-        8
-      }
-    } else if (v < 1000000000000L) {
-      if (v < 10000000000L) {
-        if (v < 1000000000L) {
-          9
-        } else {
-          10
-        }
-      } else if (v < 100000000000L) {
-        11
-      } else {
-        12
-      }
-    } else if (v < 1000000000000000L) {
-      if (v < 10000000000000L) {
-        13
-      } else if (v < 100000000000000L) {
-        14
-      } else {
-        15
-      }
-    } else if (v < 100000000000000000L) {
-      if (v < 10000000000000000L) {
-        16
-      } else {
-        17
-      }
-    } else if (v < 1000000000000000000L) {
-      18
-    } else {
-      19
-    }
+  var width = countDigitsIn(v)
   if (negative) {
     ++width
   }
@@ -539,6 +483,34 @@ internal inline fun Buffer.commonWriteDecimalLong(v: Long): Buffer {
   return this
 }
 
+private fun countDigitsIn(v: Long): Int {
+  val guess = ((64 - v.countLeadingZeroBits()) * 10) ushr 5
+  return guess + (if (v > DigitCountToLargestValue[guess]) 1 else 0)
+}
+
+private val DigitCountToLargestValue = longArrayOf(
+  -1, // Every value has more than 0 digits.
+  9L, // For 1 digit (index 1), the largest value is 9.
+  99L,
+  999L,
+  9999L,
+  99999L,
+  999999L,
+  9999999L,
+  99999999L,
+  999999999L,
+  9999999999L,
+  99999999999L,
+  999999999999L,
+  9999999999999L,
+  99999999999999L,
+  999999999999999L,
+  9999999999999999L,
+  99999999999999999L,
+  999999999999999999L, // For 18 digits (index 18), the largest value is 999999999999999999.
+  Long.MAX_VALUE, // For 19 digits (index 19), the largest value is MAX_VALUE.
+)
+
 internal inline fun Buffer.commonWriteHexadecimalUnsignedLong(v: Long): Buffer {
   var v = v
   if (v == 0L) {
diff --git a/okio/src/commonTest/kotlin/okio/CommonBufferedSinkTest.kt b/okio/src/commonTest/kotlin/okio/CommonBufferedSinkTest.kt
index 08c093a871..e48274c9b3 100644
--- a/okio/src/commonTest/kotlin/okio/CommonBufferedSinkTest.kt
+++ b/okio/src/commonTest/kotlin/okio/CommonBufferedSinkTest.kt
@@ -264,6 +264,42 @@ class CommonBufferedSinkTest(
     assertLongDecimalString("10000000000000000", 10000000000000000L)
     assertLongDecimalString("100000000000000000", 100000000000000000L)
     assertLongDecimalString("1000000000000000000", 1000000000000000000L)
+    assertLongDecimalString("-9", -9L)
+    assertLongDecimalString("-99", -99L)
+    assertLongDecimalString("-999", -999L)
+    assertLongDecimalString("-9999", -9999L)
+    assertLongDecimalString("-99999", -99999L)
+    assertLongDecimalString("-999999", -999999L)
+    assertLongDecimalString("-9999999", -9999999L)
+    assertLongDecimalString("-99999999", -99999999L)
+    assertLongDecimalString("-999999999", -999999999L)
+    assertLongDecimalString("-9999999999", -9999999999L)
+    assertLongDecimalString("-99999999999", -99999999999L)
+    assertLongDecimalString("-999999999999", -999999999999L)
+    assertLongDecimalString("-9999999999999", -9999999999999L)
+    assertLongDecimalString("-99999999999999", -99999999999999L)
+    assertLongDecimalString("-999999999999999", -999999999999999L)
+    assertLongDecimalString("-9999999999999999", -9999999999999999L)
+    assertLongDecimalString("-99999999999999999", -99999999999999999L)
+    assertLongDecimalString("-999999999999999999", -999999999999999999L)
+    assertLongDecimalString("-10", -10L)
+    assertLongDecimalString("-100", -100L)
+    assertLongDecimalString("-1000", -1000L)
+    assertLongDecimalString("-10000", -10000L)
+    assertLongDecimalString("-100000", -100000L)
+    assertLongDecimalString("-1000000", -1000000L)
+    assertLongDecimalString("-10000000", -10000000L)
+    assertLongDecimalString("-100000000", -100000000L)
+    assertLongDecimalString("-1000000000", -1000000000L)
+    assertLongDecimalString("-10000000000", -10000000000L)
+    assertLongDecimalString("-100000000000", -100000000000L)
+    assertLongDecimalString("-1000000000000", -1000000000000L)
+    assertLongDecimalString("-10000000000000", -10000000000000L)
+    assertLongDecimalString("-100000000000000", -100000000000000L)
+    assertLongDecimalString("-1000000000000000", -1000000000000000L)
+    assertLongDecimalString("-10000000000000000", -10000000000000000L)
+    assertLongDecimalString("-100000000000000000", -100000000000000000L)
+    assertLongDecimalString("-1000000000000000000", -1000000000000000000L)
   }
 
   private fun assertLongDecimalString(string: String, value: Long) {