[PATCH] D28862: [compiler-rt] [test] Use approximate comparison on float types

[Michał Górny via Phabricator via cfe-commits]

mgorny created this revision.
Herald added a subscriber: dberris.

Use approximate comparison between the result of __divsc3()
and the canonical value calculated, to allow the possible difference of
1 representable value resulting from optimization.

For example, the value of (0.000001+j0.000001) / (-0.500000-j2.000000))
computed the canonical way without specific machine flags is:

  z = -0x1.3bce70p-21 + j0x1.7af7bcp-22

However, if -march=i386 -mfpmath=387 is used, it becomes:

  z = -0x1.3bce72p-21 + j0x1.7af7bcp-22

While this difference is insignificant, it may cause the exact
comparison used in tests to fail. Allowing the difference of one
representable value seems to be a reasonable compromise.


Repository:
  rL LLVM

https://reviews.llvm.org/D28862

Files:
  test/builtins/Unit/divsc3_test.c


Index: test/builtins/Unit/divsc3_test.c
===================================================================
--- test/builtins/Unit/divsc3_test.c
+++ test/builtins/Unit/divsc3_test.c
@@ -14,6 +14,7 @@
 #include "int_lib.h"
 #include <math.h>
 #include <complex.h>
+#include <stdbool.h>
 #include <stdio.h>
 
 // Returns: the quotient of (a + ib) / (c + id)
@@ -47,6 +48,25 @@
     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);
@@ -100,7 +120,7 @@
             {
             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;


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