Add test for QuickFDot6Div

This test will catch our (1 << 10) bug (which should be 1 << 9)

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4986

Change-Id: I25b607d1535a647284cee3b304a6f567f389e7f6
Reviewed-on: https://skia-review.googlesource.com/4986
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/tests/MathTest.cpp b/tests/MathTest.cpp
index 35b4136b44..0bd3cf5da5 100644
--- a/tests/MathTest.cpp
+++ b/tests/MathTest.cpp
@@ -9,6 +9,7 @@
 
 #include "SkColorPriv.h"
 #include "SkEndian.h"
+#include "SkFDot6.h"
 #include "SkFixed.h"
 #include "SkFloatBits.h"
 #include "SkFloatingPoint.h"
@@ -36,6 +37,38 @@ static void test_clz(skiatest::Reporter* reporter) {
     }
 }
 
+static void test_quick_div(skiatest::Reporter* reporter) {
+    /*
+    The inverse table is generated by turning on SkDebugf in the following test code
+    */
+    SkFixed storage[kInverseTableSize * 2];
+    SkFixed* table = storage + kInverseTableSize;
+
+    // SkDebugf("static const int gFDot6INVERSE[] = {");
+    for (SkFDot6 i=-kInverseTableSize; i<kInverseTableSize; i++) {
+        if (i != 0) {
+            table[i] = SkFDot6Div(SK_FDot6One, i);
+            REPORTER_ASSERT(reporter, table[i] == gFDot6INVERSE[i + kInverseTableSize]);
+        }
+        // SkDebugf("%d, ", table[i]);
+    }
+    // SkDebugf("}\n");
+
+
+    for (SkFDot6 a = -1024; a <= 1024; a++) {
+        for (SkFDot6 b = -1024; b <= 1024; b++) {
+            if (b != 0) {
+                SkFixed ourAnswer = QuickSkFDot6Div(a, b);
+                SkFixed directAnswer = SkFDot6Div(a, b);
+                REPORTER_ASSERT(reporter,
+                    (directAnswer == 0 && ourAnswer == 0) ||
+                    SkFixedDiv(SkAbs32(directAnswer - ourAnswer), SkAbs32(directAnswer)) <= 1 << 10
+                );
+            }
+        }
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static float sk_fsel(float pred, float result_ge, float result_lt) {
@@ -576,6 +609,7 @@ DEF_TEST(Math, reporter) {
 
     test_muldivround(reporter);
     test_clz(reporter);
+    test_quick_div(reporter);
 }
 
 template <typename T> struct PairRec {