src/utils.c - libavif - Git at Google

 // Copyright 2019 Joe Drago. All rights reserved.
 // SPDX-License-Identifier: BSD-2-Clause

 #include "avif/internal.h"

 #include <assert.h>
 #include <math.h>
 #include <string.h>

 float avifRoundf(float v)
 {
     return floorf(v + 0.5f);
 }

 // Thanks, Rob Pike! https://commandcenter.blogspot.nl/2012/04/byte-order-fallacy.html

 uint16_t avifHTONS(uint16_t s)
 {
     uint16_t result = 0;
     uint8_t * data = (uint8_t *)&result;
     data[0] = (s >> 8) & 0xff;
     data[1] = (s >> 0) & 0xff;
     return result;
 }

 uint16_t avifNTOHS(uint16_t s)
 {
     const uint8_t * data = (const uint8_t *)&s;
     return (uint16_t)((data[1] << 0) | (data[0] << 8));
 }

 uint16_t avifCTOHS(uint16_t s)
 {
     const uint8_t * data = (const uint8_t *)&s;
     return (uint16_t)((data[0] << 0) | (data[1] << 8));
 }

 uint32_t avifHTONL(uint32_t l)
 {
     uint32_t result = 0;
     uint8_t * data = (uint8_t *)&result;
     data[0] = (l >> 24) & 0xff;
     data[1] = (l >> 16) & 0xff;
     data[2] = (l >> 8) & 0xff;
     data[3] = (l >> 0) & 0xff;
     return result;
 }

 uint32_t avifNTOHL(uint32_t l)
 {
     const uint8_t * data = (const uint8_t *)&l;
     return ((uint32_t)data[3] << 0) | ((uint32_t)data[2] << 8) | ((uint32_t)data[1] << 16) | ((uint32_t)data[0] << 24);
 }

 uint32_t avifCTOHL(uint32_t l)
 {
     const uint8_t * data = (const uint8_t *)&l;
     return ((uint32_t)data[0] << 0) | ((uint32_t)data[1] << 8) | ((uint32_t)data[2] << 16) | ((uint32_t)data[3] << 24);
 }

 uint64_t avifHTON64(uint64_t l)
 {
     uint64_t result = 0;
     uint8_t * data = (uint8_t *)&result;
     data[0] = (l >> 56) & 0xff;
     data[1] = (l >> 48) & 0xff;
     data[2] = (l >> 40) & 0xff;
     data[3] = (l >> 32) & 0xff;
     data[4] = (l >> 24) & 0xff;
     data[5] = (l >> 16) & 0xff;
     data[6] = (l >> 8) & 0xff;
     data[7] = (l >> 0) & 0xff;
     return result;
 }

 uint64_t avifNTOH64(uint64_t l)
 {
     const uint8_t * data = (const uint8_t *)&l;
     return ((uint64_t)data[7] << 0) | ((uint64_t)data[6] << 8) | ((uint64_t)data[5] << 16) | ((uint64_t)data[4] << 24) |
            ((uint64_t)data[3] << 32) | ((uint64_t)data[2] << 40) | ((uint64_t)data[1] << 48) | ((uint64_t)data[0] << 56);
 }

 AVIF_ARRAY_DECLARE(avifArrayInternal, uint8_t, ptr);

 // On error, this function must set arr->ptr to NULL and both arr->count and arr->capacity to 0.
 avifBool avifArrayCreate(void * arrayStruct, uint32_t elementSize, uint32_t initialCapacity)
 {
     avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
     arr->elementSize = elementSize ? elementSize : 1;
     arr->count = 0;
     arr->capacity = initialCapacity;
     size_t byteCount = (size_t)arr->elementSize * arr->capacity;
     arr->ptr = (uint8_t *)avifAlloc(byteCount);
     if (!arr->ptr) {
         arr->capacity = 0;
         return AVIF_FALSE;
     }
     memset(arr->ptr, 0, byteCount);
     return AVIF_TRUE;
 }

 void * avifArrayPush(void * arrayStruct)
 {
     avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
     if (arr->count == arr->capacity) {
         uint8_t * oldPtr = arr->ptr;
         size_t oldByteCount = (size_t)arr->elementSize * arr->capacity;
         arr->ptr = (uint8_t *)avifAlloc(oldByteCount * 2);
         if (arr->ptr == NULL) {
             return NULL;
         }
         memset(arr->ptr + oldByteCount, 0, oldByteCount);
         memcpy(arr->ptr, oldPtr, oldByteCount);
         arr->capacity *= 2;
         avifFree(oldPtr);
     }
     ++arr->count;
     return &arr->ptr[(arr->count - 1) * (size_t)arr->elementSize];
 }

 void avifArrayPop(void * arrayStruct)
 {
     avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
     assert(arr->count > 0);
     --arr->count;
     memset(&arr->ptr[arr->count * (size_t)arr->elementSize], 0, arr->elementSize);
 }

 void avifArrayDestroy(void * arrayStruct)
 {
     avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
     if (arr->ptr) {
         avifFree(arr->ptr);
         arr->ptr = NULL;
     }
     memset(arr, 0, sizeof(avifArrayInternal));
 }

 // |a| and |b| hold int32_t values. The int64_t type is used so that we can negate INT32_MIN without
 // overflowing int32_t.
 static int64_t calcGCD(int64_t a, int64_t b)
 {
     if (a < 0) {
         a *= -1;
     }
     if (b < 0) {
         b *= -1;
     }
     while (b != 0) {
         int64_t r = a % b;
         a = b;
         b = r;
     }
     return a;
 }

 void avifFractionSimplify(avifFraction * f)
 {
     int64_t gcd = calcGCD(f->n, f->d);
     if (gcd > 1) {
         f->n = (int32_t)(f->n / gcd);
         f->d = (int32_t)(f->d / gcd);
     }
 }

 static avifBool overflowsInt32(int64_t x)
 {
     return (x < INT32_MIN) || (x > INT32_MAX);
 }

 avifBool avifFractionCD(avifFraction * a, avifFraction * b)
 {
     avifFractionSimplify(a);
     avifFractionSimplify(b);
     if (a->d != b->d) {
         const int64_t ad = a->d;
         const int64_t bd = b->d;
         const int64_t anNew = a->n * bd;
         const int64_t adNew = a->d * bd;
         const int64_t bnNew = b->n * ad;
         const int64_t bdNew = b->d * ad;
         if (overflowsInt32(anNew) || overflowsInt32(adNew) || overflowsInt32(bnNew) || overflowsInt32(bdNew)) {
             return AVIF_FALSE;
         }
         a->n = (int32_t)anNew;
         a->d = (int32_t)adNew;
         b->n = (int32_t)bnNew;
         b->d = (int32_t)bdNew;
     }
     return AVIF_TRUE;
 }

 avifBool avifFractionAdd(avifFraction a, avifFraction b, avifFraction * result)
 {
     if (!avifFractionCD(&a, &b)) {
         return AVIF_FALSE;
     }

     const int64_t resultN = (int64_t)a.n + b.n;
     if (overflowsInt32(resultN)) {
         return AVIF_FALSE;
     }
     result->n = (int32_t)resultN;
     result->d = a.d;

     avifFractionSimplify(result);
     return AVIF_TRUE;
 }

 avifBool avifFractionSub(avifFraction a, avifFraction b, avifFraction * result)
 {
     if (!avifFractionCD(&a, &b)) {
         return AVIF_FALSE;
     }

     const int64_t resultN = (int64_t)a.n - b.n;
     if (overflowsInt32(resultN)) {
         return AVIF_FALSE;
     }
     result->n = (int32_t)resultN;
     result->d = a.d;

     avifFractionSimplify(result);
     return AVIF_TRUE;
 }

 static avifBool avifDoubleToUnsignedFractionImpl(double v, uint32_t maxNumerator, uint32_t * numerator, uint32_t * denominator)
 {
     if (isnan(v) || v < 0 || v > maxNumerator) {
         return AVIF_FALSE;
     }

     // Maximum denominator: makes sure that the numerator is <= maxNumerator and the denominator is <= UINT32_MAX.
     const uint32_t maxD = (v <= 1) ? UINT32_MAX : (uint32_t)floor(maxNumerator / v);

     // Find the best approximation of v as a fraction using continued fractions, see
     // https://en.wikipedia.org/wiki/Continued_fraction
     *denominator = 1;
     uint32_t previousD = 0;
     double currentV = v - floor(v);
     int iter = 0;
     // Set a maximum number of iterations to be safe. Most numbers should
     // converge in less than ~20 iterations.
     // The golden ratio is the worst case and takes 39 iterations.
     const int maxIter = 39;
     while (iter < maxIter) {
         const double numeratorDouble = (double)(*denominator) * v;
         assert(numeratorDouble <= maxNumerator);
         *numerator = (uint32_t)round(numeratorDouble);
         if (fabs(numeratorDouble - (*numerator)) == 0.0) {
             return AVIF_TRUE;
         }
         currentV = 1.0 / currentV;
         const double newD = previousD + floor(currentV) * (*denominator);
         if (newD > (double)maxD) {
             // This is the best we can do with a denominator <= max_d.
             return AVIF_TRUE;
         }
         previousD = *denominator;
         assert(newD <= UINT32_MAX);
         *denominator = (uint32_t)newD;
         currentV -= floor(currentV);
         ++iter;
     }
     // Maximum number of iterations reached, return what we've found.
     // For max_iter >= 39 we shouldn't get here. max_iter can be set
     // to a lower value to speed up the algorithm if needed.
     *numerator = (uint32_t)round((double)(*denominator) * v);
     return AVIF_TRUE;
 }

 avifBool avifDoubleToSignedFraction(double v, avifSignedFraction * fraction)
 {
     uint32_t positive_numerator;
     if (!avifDoubleToUnsignedFractionImpl(fabs(v), INT32_MAX, &positive_numerator, &fraction->d)) {
         return AVIF_FALSE;
     }
     fraction->n = (int32_t)positive_numerator;
     if (v < 0) {
         fraction->n *= -1;
     }
     return AVIF_TRUE;
 }

 avifBool avifDoubleToUnsignedFraction(double v, avifUnsignedFraction * fraction)
 {
     return avifDoubleToUnsignedFractionImpl(v, UINT32_MAX, &fraction->n, &fraction->d);
 }
	// Copyright 2019 Joe Drago. All rights reserved.
	// SPDX-License-Identifier: BSD-2-Clause

	#include "avif/internal.h"

	#include <assert.h>
	#include <math.h>
	#include <string.h>

	float avifRoundf(float v)
	{
	return floorf(v + 0.5f);
	}

	// Thanks, Rob Pike! https://commandcenter.blogspot.nl/2012/04/byte-order-fallacy.html

	uint16_t avifHTONS(uint16_t s)
	{
	uint16_t result = 0;
	uint8_t * data = (uint8_t *)&result;
	data[0] = (s >> 8) & 0xff;
	data[1] = (s >> 0) & 0xff;
	return result;
	}

	uint16_t avifNTOHS(uint16_t s)
	{
	const uint8_t * data = (const uint8_t *)&s;
	return (uint16_t)((data[1] << 0) \| (data[0] << 8));
	}

	uint16_t avifCTOHS(uint16_t s)
	{
	const uint8_t * data = (const uint8_t *)&s;
	return (uint16_t)((data[0] << 0) \| (data[1] << 8));
	}

	uint32_t avifHTONL(uint32_t l)
	{
	uint32_t result = 0;
	uint8_t * data = (uint8_t *)&result;
	data[0] = (l >> 24) & 0xff;
	data[1] = (l >> 16) & 0xff;
	data[2] = (l >> 8) & 0xff;
	data[3] = (l >> 0) & 0xff;
	return result;
	}

	uint32_t avifNTOHL(uint32_t l)
	{
	const uint8_t * data = (const uint8_t *)&l;
	return ((uint32_t)data[3] << 0) \| ((uint32_t)data[2] << 8) \| ((uint32_t)data[1] << 16) \| ((uint32_t)data[0] << 24);
	}

	uint32_t avifCTOHL(uint32_t l)
	{
	const uint8_t * data = (const uint8_t *)&l;
	return ((uint32_t)data[0] << 0) \| ((uint32_t)data[1] << 8) \| ((uint32_t)data[2] << 16) \| ((uint32_t)data[3] << 24);
	}

	uint64_t avifHTON64(uint64_t l)
	{
	uint64_t result = 0;
	uint8_t * data = (uint8_t *)&result;
	data[0] = (l >> 56) & 0xff;
	data[1] = (l >> 48) & 0xff;
	data[2] = (l >> 40) & 0xff;
	data[3] = (l >> 32) & 0xff;
	data[4] = (l >> 24) & 0xff;
	data[5] = (l >> 16) & 0xff;
	data[6] = (l >> 8) & 0xff;
	data[7] = (l >> 0) & 0xff;
	return result;
	}

	uint64_t avifNTOH64(uint64_t l)
	{
	const uint8_t * data = (const uint8_t *)&l;
	return ((uint64_t)data[7] << 0) \| ((uint64_t)data[6] << 8) \| ((uint64_t)data[5] << 16) \| ((uint64_t)data[4] << 24) \|
	((uint64_t)data[3] << 32) \| ((uint64_t)data[2] << 40) \| ((uint64_t)data[1] << 48) \| ((uint64_t)data[0] << 56);
	}

	AVIF_ARRAY_DECLARE(avifArrayInternal, uint8_t, ptr);

	// On error, this function must set arr->ptr to NULL and both arr->count and arr->capacity to 0.
	avifBool avifArrayCreate(void * arrayStruct, uint32_t elementSize, uint32_t initialCapacity)
	{
	avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
	arr->elementSize = elementSize ? elementSize : 1;
	arr->count = 0;
	arr->capacity = initialCapacity;
	size_t byteCount = (size_t)arr->elementSize * arr->capacity;
	arr->ptr = (uint8_t *)avifAlloc(byteCount);
	if (!arr->ptr) {
	arr->capacity = 0;
	return AVIF_FALSE;
	}
	memset(arr->ptr, 0, byteCount);
	return AVIF_TRUE;
	}

	void * avifArrayPush(void * arrayStruct)
	{
	avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
	if (arr->count == arr->capacity) {
	uint8_t * oldPtr = arr->ptr;
	size_t oldByteCount = (size_t)arr->elementSize * arr->capacity;
	arr->ptr = (uint8_t )avifAlloc(oldByteCount 2);
	if (arr->ptr == NULL) {
	return NULL;
	}
	memset(arr->ptr + oldByteCount, 0, oldByteCount);
	memcpy(arr->ptr, oldPtr, oldByteCount);
	arr->capacity *= 2;
	avifFree(oldPtr);
	}
	++arr->count;
	return &arr->ptr[(arr->count - 1) * (size_t)arr->elementSize];
	}

	void avifArrayPop(void * arrayStruct)
	{
	avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
	assert(arr->count > 0);
	--arr->count;
	memset(&arr->ptr[arr->count * (size_t)arr->elementSize], 0, arr->elementSize);
	}

	void avifArrayDestroy(void * arrayStruct)
	{
	avifArrayInternal * arr = (avifArrayInternal *)arrayStruct;
	if (arr->ptr) {
	avifFree(arr->ptr);
	arr->ptr = NULL;
	}
	memset(arr, 0, sizeof(avifArrayInternal));
	}

	// \|a\| and \|b\| hold int32_t values. The int64_t type is used so that we can negate INT32_MIN without
	// overflowing int32_t.
	static int64_t calcGCD(int64_t a, int64_t b)
	{
	if (a < 0) {
	a *= -1;
	}
	if (b < 0) {
	b *= -1;
	}
	while (b != 0) {
	int64_t r = a % b;
	a = b;
	b = r;
	}
	return a;
	}

	void avifFractionSimplify(avifFraction * f)
	{
	int64_t gcd = calcGCD(f->n, f->d);
	if (gcd > 1) {
	f->n = (int32_t)(f->n / gcd);
	f->d = (int32_t)(f->d / gcd);
	}
	}

	static avifBool overflowsInt32(int64_t x)
	{
	return (x < INT32_MIN) \|\| (x > INT32_MAX);
	}

	avifBool avifFractionCD(avifFraction * a, avifFraction * b)
	{
	avifFractionSimplify(a);
	avifFractionSimplify(b);
	if (a->d != b->d) {
	const int64_t ad = a->d;
	const int64_t bd = b->d;
	const int64_t anNew = a->n * bd;
	const int64_t adNew = a->d * bd;
	const int64_t bnNew = b->n * ad;
	const int64_t bdNew = b->d * ad;
	if (overflowsInt32(anNew) \|\| overflowsInt32(adNew) \|\| overflowsInt32(bnNew) \|\| overflowsInt32(bdNew)) {
	return AVIF_FALSE;
	}
	a->n = (int32_t)anNew;
	a->d = (int32_t)adNew;
	b->n = (int32_t)bnNew;
	b->d = (int32_t)bdNew;
	}
	return AVIF_TRUE;
	}

	avifBool avifFractionAdd(avifFraction a, avifFraction b, avifFraction * result)
	{
	if (!avifFractionCD(&a, &b)) {
	return AVIF_FALSE;
	}

	const int64_t resultN = (int64_t)a.n + b.n;
	if (overflowsInt32(resultN)) {
	return AVIF_FALSE;
	}
	result->n = (int32_t)resultN;
	result->d = a.d;

	avifFractionSimplify(result);
	return AVIF_TRUE;
	}

	avifBool avifFractionSub(avifFraction a, avifFraction b, avifFraction * result)
	{
	if (!avifFractionCD(&a, &b)) {
	return AVIF_FALSE;
	}

	const int64_t resultN = (int64_t)a.n - b.n;
	if (overflowsInt32(resultN)) {
	return AVIF_FALSE;
	}
	result->n = (int32_t)resultN;
	result->d = a.d;

	avifFractionSimplify(result);
	return AVIF_TRUE;
	}

	static avifBool avifDoubleToUnsignedFractionImpl(double v, uint32_t maxNumerator, uint32_t * numerator, uint32_t * denominator)
	{
	if (isnan(v) \|\| v < 0 \|\| v > maxNumerator) {
	return AVIF_FALSE;
	}

	// Maximum denominator: makes sure that the numerator is <= maxNumerator and the denominator is <= UINT32_MAX.
	const uint32_t maxD = (v <= 1) ? UINT32_MAX : (uint32_t)floor(maxNumerator / v);

	// Find the best approximation of v as a fraction using continued fractions, see
	// https://en.wikipedia.org/wiki/Continued_fraction
	*denominator = 1;
	uint32_t previousD = 0;
	double currentV = v - floor(v);
	int iter = 0;
	// Set a maximum number of iterations to be safe. Most numbers should
	// converge in less than ~20 iterations.
	// The golden ratio is the worst case and takes 39 iterations.
	const int maxIter = 39;
	while (iter < maxIter) {
	const double numeratorDouble = (double)(denominator) v;
	assert(numeratorDouble <= maxNumerator);
	*numerator = (uint32_t)round(numeratorDouble);
	if (fabs(numeratorDouble - (*numerator)) == 0.0) {
	return AVIF_TRUE;
	}
	currentV = 1.0 / currentV;
	const double newD = previousD + floor(currentV) * (*denominator);
	if (newD > (double)maxD) {
	// This is the best we can do with a denominator <= max_d.
	return AVIF_TRUE;
	}
	previousD = *denominator;
	assert(newD <= UINT32_MAX);
	*denominator = (uint32_t)newD;
	currentV -= floor(currentV);
	++iter;
	}
	// Maximum number of iterations reached, return what we've found.
	// For max_iter >= 39 we shouldn't get here. max_iter can be set
	// to a lower value to speed up the algorithm if needed.
	numerator = (uint32_t)round((double)(denominator) * v);
	return AVIF_TRUE;
	}

	avifBool avifDoubleToSignedFraction(double v, avifSignedFraction * fraction)
	{
	uint32_t positive_numerator;
	if (!avifDoubleToUnsignedFractionImpl(fabs(v), INT32_MAX, &positive_numerator, &fraction->d)) {
	return AVIF_FALSE;
	}
	fraction->n = (int32_t)positive_numerator;
	if (v < 0) {
	fraction->n *= -1;
	}
	return AVIF_TRUE;
	}

	avifBool avifDoubleToUnsignedFraction(double v, avifUnsignedFraction * fraction)
	{
	return avifDoubleToUnsignedFractionImpl(v, UINT32_MAX, &fraction->n, &fraction->d);
	}