#107 sqrt of large number

MikeMcl · MikeMcl · commit d54f97e6e77a · 2018-10-07T23:20:39.000+01:00
diff --git a/big.js b/big.js
@@ -766,17 +766,18 @@
     if (s < 0) throw Error(NAME + 'No square root');
 
     // Estimate.
-    s = Math.sqrt(x.toString());
+    s = Math.sqrt(x + '');
 
     // Math.sqrt underflow/overflow?
-    // Re-estimate: pass x to Math.sqrt as integer, then adjust the result exponent.
+    // Re-estimate: pass x coefficient to Math.sqrt as integer, then adjust the result exponent.
     if (s === 0 || s === 1 / 0) {
       c = x.c.join('');
       if (!(c.length + e & 1)) c += '0';
-      r = new Big(Math.sqrt(c).toString());
-      r.e = ((e + 1) / 2 | 0) - (e < 0 || e & 1);
+      s = Math.sqrt(c);
+      e = ((e + 1) / 2 | 0) - (e < 0 || e & 1);
+      r = new Big((s == 1 / 0 ? '1e' : (s = s.toExponential()).slice(0, s.indexOf('e') + 1)) + e);
     } else {
-      r = new Big(s.toString());
+      r = new Big(s);
     }
 
     e = r.e + (Big.DP += 4);
diff --git a/big.mjs b/big.mjs
@@ -763,17 +763,18 @@ P.sqrt = function () {
   if (s < 0) throw Error(NAME + 'No square root');
 
   // Estimate.
-  s = Math.sqrt(x.toString());
+  s = Math.sqrt(x + '');
 
   // Math.sqrt underflow/overflow?
-  // Re-estimate: pass x to Math.sqrt as integer, then adjust the result exponent.
+  // Re-estimate: pass x coefficient to Math.sqrt as integer, then adjust the result exponent.
   if (s === 0 || s === 1 / 0) {
     c = x.c.join('');
     if (!(c.length + e & 1)) c += '0';
-    r = new Big(Math.sqrt(c).toString());
-    r.e = ((e + 1) / 2 | 0) - (e < 0 || e & 1);
+    s = Math.sqrt(c);
+    e = ((e + 1) / 2 | 0) - (e < 0 || e & 1);
+    r = new Big((s == 1 / 0 ? '1e' : (s = s.toExponential()).slice(0, s.indexOf('e') + 1)) + e);
   } else {
-    r = new Big(s.toString());
+    r = new Big(s);
   }
 
   e = r.e + (Big.DP += 4);
diff --git a/test/sqrt.js b/test/sqrt.js
@@ -781,6 +781,11 @@ var count = (function sqrt(Big) {
     Big.DP = 2;
     T('0.04', 0.001);
 
+    Big.DP = 20;
+    Big.RM = 0;
+    T('9.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999e+179', new Big('1e360').minus(1));
+    //T('9.999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999e+499', new Big('1e1000').minus(1));
+
     log('\n ' + passed + ' of ' + total + ' tests passed in ' + (+new Date() - start) + ' ms \n');
     return [passed, total];;
 })(this.Big);
