#338 [BUGFIX] exponentiatedBy: ensure 0**-n === Infinity for very large n

MikeMcl · MikeMcl · commit 909f94a6c893 · 2022-12-04T12:41:32.000Z
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,8 +1,12 @@
+#### 9.1.1
+* 04/12/22
+* #338 [BUGFIX] `exponentiatedBy`: ensure `0**-n === Infinity` for very large `n`.
+
 #### 9.1.0
 * 08/08/22
 * #329 Remove `import` example.
 * #277 Resolve lint warnings and add number `toString` note.
-* Correct `decimalPlaces()` return type in *bignumber.d.ts*. 
+* Correct `decimalPlaces()` return type in *bignumber.d.ts*.
 * Add ES module global `crypto` example.
 * #322 Add `exports` field to *package.json*.
 * #251 (#308) Amend *bignumber.d.ts* to allow instantiating a BigNumber without `new`.
diff --git a/bignumber.js b/bignumber.js
@@ -1706,7 +1706,7 @@
 
         // The sign of the result of pow when x is negative depends on the evenness of n.
         // If +n overflows to ±Infinity, the evenness of n would be not be known.
-        y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? 2 - isOdd(n) : +valueOf(n)));
+        y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? n.s * (2 - isOdd(n)) : +valueOf(n)));
         return m ? y.mod(m) : y;
       }
 
@@ -2012,7 +2012,7 @@
         xc = yc;
         yc = t;
         y.s = -y.s;
-      }  
+      }
 
       b = (j = yc.length) - (i = xc.length);
 
@@ -2173,7 +2173,7 @@
         i = xcL;
         xcL = ycL;
         ycL = i;
-      }  
+      }
 
       // Initialise the result array with zeros.
       for (i = xcL + ycL, zc = []; i--; zc.push(0));
@@ -2299,7 +2299,7 @@
         yc = xc;
         xc = t;
         b = a;
-      }  
+      }
 
       // Only start adding at yc.length - 1 as the further digits of xc can be ignored.
       for (a = 0; b;) {
@@ -2590,7 +2590,7 @@
           g1 = g2;
           g2 = i;
           len -= i;
-        }  
+        }
 
         if (g1 > 0 && len > 0) {
           i = len % g1 || g1;
diff --git a/bignumber.mjs b/bignumber.mjs
@@ -1703,7 +1703,7 @@ function clone(configObject) {
 
       // The sign of the result of pow when x is negative depends on the evenness of n.
       // If +n overflows to ±Infinity, the evenness of n would be not be known.
-      y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? 2 - isOdd(n) : +valueOf(n)));
+      y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? n.s * (2 - isOdd(n)) : +valueOf(n)));
       return m ? y.mod(m) : y;
     }
 
diff --git a/test/methods/exponentiatedBy.js b/test/methods/exponentiatedBy.js
@@ -40,6 +40,8 @@ Test('exponentiatedBy', function () {
     t('NaN', 0, NaN);
     t('0', 0, Infinity);
     t('Infinity', 0, -Infinity);
+    t('Infinity', 0, '-123456789012345');
+    t('Infinity', 0, '-12345678901234567890123456789012345678901234567890');
 
     //-0
     t('1', -0, +0);
@@ -51,6 +53,8 @@ Test('exponentiatedBy', function () {
     t('NaN', -0, NaN);
     t('0', -0, Infinity);
     t('Infinity', -0, -Infinity);
+    t('-Infinity', -0, '-123456789012345');
+    t('Infinity', -0, '-12345678901234567890123456789012345678901234567890');
 
     // 1
     t('1', 1, +0);

Original file line number	Diff line number	Diff line change
`@@ -1703,7 +1703,7 @@ function clone(configObject) {`
`1703`	`1703`
`1704`	`1704`	`// The sign of the result of pow when x is negative depends on the evenness of n.`
`1705`	`1705`	`// If +n overflows to ±Infinity, the evenness of n would be not be known.`
`1706`		`- y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? 2 - isOdd(n) : +valueOf(n)));`
	`1706`	`+ y = new BigNumber(Math.pow(+valueOf(x), nIsBig ? n.s * (2 - isOdd(n)) : +valueOf(n)));`
`1707`	`1707`	`return m ? y.mod(m) : y;`
`1708`	`1708`	`}`
`1709`	`1709`