[corelib] Fix for BigInt.toDouble() crash

Bug: 41819
Change-Id: Ied24b42728e1da0d713fe971386d4ef6a023333e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147349
Reviewed-by: Bob Nystrom <[email protected]>
Commit-Queue: Stephen Adams <[email protected]>

Author: rakudrama

sdk/lib/_internal/js_dev_runtime/patch/core_patch.dart

@@ -2825,7 +2825,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

sdk/lib/_internal/js_runtime/lib/core_patch.dart

@@ -2738,7 +2738,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

sdk/lib/_internal/vm/lib/bigint_patch.dart

@@ -2409,7 +2409,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

sdk_nnbd/lib/_internal/js_dev_runtime/patch/core_patch.dart

@@ -2830,7 +2830,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

sdk_nnbd/lib/_internal/js_runtime/lib/core_patch.dart

@@ -2760,7 +2760,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

sdk_nnbd/lib/_internal/vm/lib/bigint_patch.dart

@@ -2413,7 +2413,7 @@ class _BigIntImpl implements BigInt {
           // There is already one in the cachedBits.
           roundUp();
         } else {
-          for (int i = digitIndex; digitIndex >= 0; i--) {
+          for (int i = digitIndex; i >= 0; i--) {
             if (_digits[i] != 0) {
               roundUp();
               break;

tests/corelib/bigint_test.dart

@@ -1039,6 +1039,13 @@ void testFromToDouble() {
 
   Expect.equals(BigInt.zero, new BigInt.from(0.9999999999999999));
   Expect.equals(BigInt.zero, new BigInt.from(-0.9999999999999999));
+
+  // Regression test for http://dartbug.com/41819
+  // Rounding edge case where last digit causes rounding.
+  Expect.equals(-3.69616463331328e+27,
+      BigInt.parse("-3696164633313280000000000000").toDouble());
+  Expect.equals(-3.6961646333132803e+27,
+      BigInt.parse("-3696164633313280000000000001").toDouble());
 }
 
 main() {

tests/corelib_2/bigint_test.dart

@@ -1039,6 +1039,13 @@ void testFromToDouble() {
 
   Expect.equals(BigInt.zero, new BigInt.from(0.9999999999999999));
   Expect.equals(BigInt.zero, new BigInt.from(-0.9999999999999999));
+
+  // Regression test for http://dartbug.com/41819
+  // Rounding edge case where last digit causes rounding.
+  Expect.equals(-3.69616463331328e+27,
+      BigInt.parse("-3696164633313280000000000000").toDouble());
+  Expect.equals(-3.6961646333132803e+27,
+      BigInt.parse("-3696164633313280000000000001").toDouble());
 }
 
 main() {