Fix frexp does not accept negative numbers

Add frexp unit tests

2 files changed, 47 insertions, 1 deletions

diff --git a/src/library.js b/src/library.js
index 51c4c5cb..5e2cb482 100644
--- a/src/library.js
+++ b/src/library.js
@@ -5600,10 +5600,15 @@ LibraryManager.library = {
   frexp: function(x, exp_addr) {
     var sig = 0, exp_ = 0;
     if (x !== 0) {
+      var sign = 1;
+      if (x < 0) {
+        x = -x;
+        sign = -1;
+      }
       var raw_exp = Math.log(x)/Math.log(2);
       exp_ = Math.ceil(raw_exp);
       if (exp_ === raw_exp) exp_ += 1;
-      sig = x/Math.pow(2, exp_);
+      sig = sign*x/Math.pow(2, exp_);
     }
     {{{ makeSetValue('exp_addr', 0, 'exp_', 'i32') }}}
     return sig;
diff --git a/tests/runner.py b/tests/runner.py
index 47c1f1be..803c1d2b 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -1916,6 +1916,47 @@ Succeeded!
         expected = open(path_from_root('tests', 'hyperbolic', 'output.txt'), 'r').read()
         self.do_run(src, expected)
 
+    def test_frexp(self):
+        src = '''
+          #include <stdio.h>
+          #include <math.h>
+          #include <assert.h>
+
+          static const double tol=1e-16;
+
+          void test_value(double value)
+          {
+            int exponent;
+            double x=frexp(value, &exponent);
+            double expected=x*pow(2.0, exponent);
+
+            printf("%f=%f*2^%d\\n", value, x, exponent);
+
+            assert(fabs(expected-value)<tol);
+            assert(x==0 || (fabs(x)>=5e-1 && fabs(x)<1)); // x has a magnitude in the interval [1/2, 1)
+          }
+
+          int main()
+          {
+            test_value(0);
+            test_value(100.1);
+            test_value(-100.1);
+            test_value(.5);
+            test_value(-.5);
+            test_value(1-1e-16);
+            test_value(-(1-1e-16));
+
+            return 0;
+          }
+        '''
+        self.do_run(src, '''0.000000=0.000000*2^0
+100.100000=0.782031*2^7
+-100.100000=-0.782031*2^7
+0.500000=0.500000*2^0
+-0.500000=-0.500000*2^0
+1.000000=1.000000*2^0
+-1.000000=-1.000000*2^0''')
+
     def test_getgep(self):
         # Generated code includes getelementptr (getelementptr, 0, 1), i.e., GEP as the first param to GEP
         src = '''