For *ToFixed, in debug mode, assert that the value is in range.

include/core/SkFixed.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkFixed_DEFINED
 #define SkFixed_DEFINED
 
@@ skipping 11 matching lines @@
 typedef int32_t             SkFixed;
 #define SK_Fixed1           (1 << 16)
 #define SK_FixedHalf        (1 << 15)
 #define SK_FixedMax         (0x7FFFFFFF)
 #define SK_FixedMin         (-SK_FixedMax)
 #define SK_FixedPI          (0x3243F)
 #define SK_FixedSqrt2       (92682)
 #define SK_FixedTanPIOver8  (0x6A0A)
 #define SK_FixedRoot2Over2  (0xB505)
 
-#define SkFixedToFloat(x)   ((x) * 1.52587890625e-5f)
-#define SkFloatToFixed(x)   ((SkFixed)((x) * SK_Fixed1))
+#define SkFixedToFloat(x)         ((x) * 1.52587890625e-5f)
+#define SkFloatToFixed_Unsafe(x)  ((SkFixed)((x) * SK_Fixed1))
+
+#ifdef SK_DEBUG
+    static inline SkFixed SkFloatToFixed(float x) {

[mtklein, 2016/03/22 12:38:02]

It should be fine to use this definition in Debug and Release.  SkASSERT does
nothing in Release mode, and the rest will inline just like the macro.

+        const SkFixed result = SkFloatToFixed_Unsafe(x);
+        SkASSERT(truncf(x * SK_Fixed1) == static_cast<float>(result));
+        return result;
+    }
+#else
+    #define SkFloatToFixed(x)  SkFloatToFixed_Unsafe(x)
+#endif
 
 // Pins over/under flows to SK_FixedMax/SK_FixedMin (slower than just a cast).
 static inline SkFixed SkFloatPinToFixed(float x) {
     x *= SK_Fixed1;
     // Casting float to int outside the range of the target type (int32_t) is undefined behavior.
     if (x >= SK_FixedMax) return SK_FixedMax;
     if (x <= SK_FixedMin) return SK_FixedMin;
     const SkFixed result = static_cast<SkFixed>(x);
     SkASSERT(truncf(x) == static_cast<float>(result));
     return result;
 }
 
+#define SkFixedToDouble(x)         ((x) * 1.52587890625e-5)
+#define SkDoubleToFixed_Unsafe(x)  ((SkFixed)((x) * SK_Fixed1))
+
 #ifdef SK_DEBUG

[mtklein, 2016/03/22 12:38:02]

Ditto.

-    static inline SkFixed SkFloatToFixed_Check(float x) {
-        int64_t n64 = (int64_t)(x * SK_Fixed1);
-        SkFixed n32 = (SkFixed)n64;
-        SkASSERT(n64 == n32);
-        return n32;
+    static inline SkFixed SkDoubleToFixed(double x) {
+        const SkFixed result = SkDoubleToFixed_Unsafe(x);
+        SkASSERT(trunc(x * SK_Fixed1) == static_cast<double>(result));
+        return result;
     }
 #else
-    #define SkFloatToFixed_Check(x) SkFloatToFixed(x)
+    #define SkDoubleToFixed(x)  SkDoubleToFixed_Unsafe(x)
 #endif
 
-#define SkFixedToDouble(x)  ((x) * 1.52587890625e-5)
-#define SkDoubleToFixed(x)  ((SkFixed)((x) * SK_Fixed1))
-
 // Pins over/under flows to SK_FixedMax/SK_FixedMin (slower than just a cast).
 static inline SkFixed SkDoublePinToFixed(double x) {
     x *= SK_Fixed1;
     // Casting double to int outside the range of the target type (int32_t) is undefined behavior.
     if (x >= SK_FixedMax) return SK_FixedMax;
     if (x <= SK_FixedMin) return SK_FixedMin;
     const SkFixed result = static_cast<SkFixed>(x);
     SkASSERT(trunc(x) == static_cast<double>(result));
     return result;
 }
@@ skipping 75 matching lines @@
             "orr    %0, %0, %2, lsl #16     \n"
             : "=r"(x), "=&r"(y), "=r"(t)
             : "r"(x), "1"(y)
             :
             );
         return x;
     }
     #undef SkFixedMul
     #define SkFixedMul(x, y)        SkFixedMul_arm(x, y)
 
-    #undef SkFloatToFixed
-    #define SkFloatToFixed(x)  SkFloatToFixed_arm(x)
+    #undef SkFloatToFixed_Unsafe
+    #define SkFloatToFixed_Unsafe(x)  SkFloatToFixed_arm(x)

[mtklein, 2016/03/22 12:38:02]

Can you double check that SkFloatToFixed still calls this SkFloatToFixed_arm()
code?  I don't remember enough about macros to know if it works or not, but I
suspect it doesn't (the redefinition would only apply for later code, right?).

 #endif
 
 ///////////////////////////////////////////////////////////////////////////////
 
 typedef int64_t SkFixed3232;   // 32.32
 
-#define SkIntToFixed3232(x)       (SkLeftShift((SkFixed3232)(x), 32))
-#define SkFixed3232ToInt(x)       ((int)((x) >> 32))
-#define SkFixedToFixed3232(x)     (SkLeftShift((SkFixed3232)(x), 16))
-#define SkFixed3232ToFixed(x)     ((SkFixed)((x) >> 16))
-#define SkFloatToFixed3232(x)     ((SkFixed3232)((x) * (65536.0f * 65536.0f)))
+#define SK_Fixed3232_1                (static_cast<SkFixed3232>(1) << 32)
+#define SkIntToFixed3232(x)           (SkLeftShift((SkFixed3232)(x), 32))
+#define SkFixed3232ToInt(x)           ((int)((x) >> 32))
+#define SkFixedToFixed3232(x)         (SkLeftShift((SkFixed3232)(x), 16))
+#define SkFixed3232ToFixed(x)         ((SkFixed)((x) >> 16))
+#define SkFloatToFixed3232_Unsafe(x)  (static_cast<SkFixed3232>((x) * SK_Fixed3232_1))
+
+#ifdef SK_DEBUG

[mtklein, 2016/03/22 12:38:03]

ditto

+    static inline SkFixed3232 SkFloatToFixed3232(float x) {
+        const SkFixed3232 result = SkFloatToFixed3232_Unsafe(x);
+        SkASSERT(truncf(x * SK_Fixed3232_1) == static_cast<float>(result));
+        return result;
+    }
+#else
+    #define SkFloatToFixed3232(x)  SkFloatToFixed3232_Unsafe(x)
+#endif
 
 #define SkScalarToFixed3232(x)    SkFloatToFixed3232(x)
 
 ///////////////////////////////////////////////////////////////////////////////
 
 // 64bits wide, with a 16bit bias. Useful when accumulating lots of 16.16 so
 // we don't overflow along the way
 typedef int64_t Sk48Dot16;
 
 #define Sk48Dot16FloorToInt(x)    static_cast<int>((x) >> 16)
 
 static inline float Sk48Dot16ToScalar(Sk48Dot16 x) {
     return static_cast<float>(x * 1.5258789e-5);  // x * (1.0f / (1 << 16))
 }
 #define SkFloatTo48Dot16(x)       (static_cast<Sk48Dot16>((x) * (1 << 16)))
 
 #define SkScalarTo48Dot16(x)      SkFloatTo48Dot16(x)
 
 #endif