[compiler-rt] [test] Use approximate comparison on float types

[erceg95]

Summary

We are resubmitting this patch (https://reviews.llvm.org/D28862) as it still causes this test of fail on Ubuntu 18.04 , Ubuntu GLIBC 2.27-3ubuntu1.

test/builtins/Unit/divsc3_test.c

 //
 // This file tests __divsc3 for the compiler_rt library.
 //
 //===----------------------------------------------------------------------===//
 
 #include "int_lib.h"
 #include <math.h>
 #include <complex.h>
+#include <stdbool.h>
 #include <stdio.h>
 
 // REQUIRES: c99-complex
 
 // Returns: the quotient of (a + ib) / (c + id)
 
 COMPILER_RT_ABI float _Complex
 __divsc3(float __a, float __b, float __c, float __d);
classify(float _Complex x)
     {
         if (crealf(x) == 0)
             return NaN;
         return non_zero_nan;
     }
     return non_zero;
 }
 
+// check for equality assuming that both real and imaginary parts
+// can differ by exactly 1 representable value, in order to handle
+// different levels of accuracy on 32-bit x86
+static bool approx_equal(float _Complex a, float _Complex b) {
+    if (a != b) {
+        float ra = __real__ a;
+        float ia = __imag__ a;
+        float rb = __real__ b;
+        float ib = __imag__ b;
+
+        if (ra != rb && nextafterf(ra, rb) != rb)
+            return false;
+        if (ia != ib && nextafterf(ia, ib) != ib)
+            return false;
+    }
+
+    return true;
+}
+
 int test__divsc3(float a, float b, float c, float d)
 {
     float _Complex r = __divsc3(a, b, c, d);
 //     printf("test__divsc3(%f, %f, %f, %f) = %f + I%f\n",
 //             a, b, c, d, crealf(r), cimagf(r));
   float _Complex dividend;
   float _Complex divisor;
   
case non_zero:
                 return 1;
             break;
         case non_zero:
             if (classify(r) != non_zero)
                 return 1;
             {
             float _Complex z = (a * c + b * d) / (c * c + d * d)
                              + (b * c - a * d) / (c * c + d * d) * _Complex_I;
-            if (r != z)
+            if (!approx_equal(r, z))
                 return 1;
             }
             break;
         case inf:
             if (classify(r) != zero)
                 return 1;
             break;
         case NaN: