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* Copyright 2016 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkScaleToSides_DEFINED
#define SkScaleToSides_DEFINED
#include "include/core/SkScalar.h"
#include "include/core/SkTypes.h"
#include <cmath>
#include <utility>
class SkScaleToSides {
// This code assumes that a and b fit in a float, and therefore the resulting smaller value
// of a and b will fit in a float. The side of the rectangle may be larger than a float.
// Scale must be less than or equal to the ratio limit / (*a + *b).
// This code assumes that NaN and Inf are never passed in.
static void AdjustRadii(double limit, double scale, SkScalar* a, SkScalar* b) {
SkASSERTF(scale < 1.0 && scale > 0.0, "scale: %g", scale);
*a = (float)((double)*a * scale);
*b = (float)((double)*b * scale);
if (*a + *b > limit) {
float* minRadius = a;
float* maxRadius = b;
// Force minRadius to be the smaller of the two.
if (*minRadius > *maxRadius) {
using std::swap;
swap(minRadius, maxRadius);
// newMinRadius must be float in order to give the actual value of the radius.
// The newMinRadius will always be smaller than limit. The largest that minRadius can be
// is 1/2 the ratio of minRadius : (minRadius + maxRadius), therefore in the resulting
// division, minRadius can be no larger than 1/2 limit + ULP. The newMinRadius can be
// 1/2 a ULP off at this point.
float newMinRadius = *minRadius;
// Because newMaxRadius is the result of a double to float conversion, it can be larger
// than limit, but only by one ULP.
float newMaxRadius = (float)(limit - newMinRadius);
// The total sum of newMinRadius and newMaxRadius can be upto 1.5 ULPs off. If the
// sum is greater than the limit then newMaxRadius may have to be reduced twice.
// Note: nextafterf is a c99 call and should be std::nextafter, but this is not
// implemented in the GCC ARM compiler.
if (newMaxRadius + newMinRadius > limit) {
newMaxRadius = nextafterf(newMaxRadius, 0.0f);
if (newMaxRadius + newMinRadius > limit) {
newMaxRadius = nextafterf(newMaxRadius, 0.0f);
*maxRadius = newMaxRadius;
SkASSERTF(*a >= 0.0f && *b >= 0.0f, "a: %g, b: %g, limit: %g, scale: %g", *a, *b, limit,
SkASSERTF(*a + *b <= limit,
"\nlimit: %.17f, sum: %.17f, a: %.10f, b: %.10f, scale: %.20f",
limit, *a + *b, *a, *b, scale);
#endif // ScaleToSides_DEFINED