Improve accuracy of UnityPrintFloat() for common cases.

src/unity.c

@@ -283,9 +283,9 @@ void UnityPrintFloat(const UNITY_DOUBLE input_number)
     else if (isinf(number)) UnityPrint("inf");
     else
     {
+        UNITY_INT32 n = 0;
         int exponent = 0;
         int decimals, digits;
-        UNITY_INT32 n;
         char buf[16];
 
         /*
@@ -295,7 +295,7 @@ void UnityPrintFloat(const UNITY_DOUBLE input_number)
          * (exactly) the remaining power of 10 and perform one more
          * multiplication or division.
          */
-        if(number < 1e6f)
+        if(number < 1.0f)
         {
             UNITY_DOUBLE factor = 1.0f;
 
@@ -313,9 +313,24 @@ void UnityPrintFloat(const UNITY_DOUBLE input_number)
 
             number /= divisor;
         }
+        else
+        {
+            /*
+             * In this range, we can split off the integer part before
+             * doing any multiplications.  This reduces rounding error by
+             * freeing up significant bits in the fractional part.
+             */
+            UNITY_DOUBLE factor = 1.0f;
+            n = (UNITY_INT32)number;
+            number -= (UNITY_DOUBLE)n;
+
+            while(n < 1000000) { n *= 10; factor *= 10.0f; exponent--; }
+
+            number *= factor;
+        }
 
         /* round to nearest integer */
-        n = ((UNITY_INT32)(number + number) + 1) / 2;
+        n += ((UNITY_INT32)(number + number) + 1) / 2;
         if (n > 9999999)
         {
             n = 1000000;

test/tests/testunity.c

@@ -4543,20 +4543,33 @@ static void printFloatValue(float f)
     /* We print all NaN's as "nan", not "-nan" */
     if(strcmp(expected, "-nan") == 0) strcpy(expected, "nan");
 
-    /* Allow for relative error of +/-2.5e-7 */
+    strcpy(expected_lower, expected);
+    strcpy(expected_lower2, expected);
+    strcpy(expected_lower3, expected);
+    strcpy(expected_higher, expected);
+    strcpy(expected_higher2, expected);
+    strcpy(expected_higher3, expected);
+
+    /* Allow for rounding differences in the last digit */
     double lower = (double)f * 0.99999995;
-    double lower2 = (double)f * 0.99999985;
-    double lower3 = (double)f * 0.99999975;
     double higher = (double)f * 1.00000005;
-    double higher2 = (double)f * 1.00000015;
-    double higher3 = (double)f * 1.00000025;
-
-    if(isfinite(lower)) sprintf(expected_lower, "%.7g", lower); else strcpy(expected_lower, expected);
-    if(isfinite(lower2)) sprintf(expected_lower2, "%.7g", lower2); else strcpy(expected_lower2, expected);
-    if(isfinite(lower3)) sprintf(expected_lower3, "%.7g", lower3); else strcpy(expected_lower3, expected);
-    if(isfinite(higher)) sprintf(expected_higher, "%.7g", higher); else strcpy(expected_higher, expected);
-    if(isfinite(higher2)) sprintf(expected_higher2, "%.7g", higher2); else strcpy(expected_higher2, expected);
-    if(isfinite(higher3)) sprintf(expected_higher3, "%.7g", higher3); else strcpy(expected_higher3, expected);
+
+    if(isfinite(lower)) sprintf(expected_lower, "%.7g", lower);
+    if(isfinite(higher)) sprintf(expected_higher, "%.7g", higher);
+
+    /* Outside [1,10000000] allow for relative error of +/-2.5e-7 */
+    if(f < 1.0 || f > 10000000)
+    {
+        double lower2 = (double)f * 0.99999985;
+        double lower3 = (double)f * 0.99999975;
+        double higher2 = (double)f * 1.00000015;
+        double higher3 = (double)f * 1.00000025;
+
+        if(isfinite(lower2)) sprintf(expected_lower2, "%.7g", lower2);
+        if(isfinite(lower3)) sprintf(expected_lower3, "%.7g", lower3);
+        if(isfinite(higher2)) sprintf(expected_higher2, "%.7g", higher2);
+        if(isfinite(higher3)) sprintf(expected_higher3, "%.7g", higher3);
+    }
 
     if (strcmp(expected, getBufferPutcharSpy()) != 0 &&
         strcmp(expected_lower, getBufferPutcharSpy()) != 0 &&