/*
  Copyright (c) 2019 Alex Diener
  
  This software is provided 'as-is', without any express or implied
  warranty. In no event will the authors be held liable for any damages
  arising from the use of this software.
  
  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:
  
  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
  
  Alex Diener alex@ludobloom.com
*/

#include "gamemath/IntegerFraction.h"
#include <limits.h>
#include <stdint.h>
#include <stdlib.h>

ifrac ifrac_fromFloat(float value) {
	uint32_t floatBits = *(uint32_t *) &value;
	int sign = (floatBits >> 31) * -2 + 1;
	unsigned int exponentBits = (floatBits >> 23) & 0xFF;
	unsigned int mantissaBits = floatBits & 0x7FFFFF;
	
	ifrac fraction;
	if (exponentBits == 0 && mantissaBits == 0) {
		// 0
		fraction.numerator = 0;
		fraction.denominator = 1;
	} else if (exponentBits == 0xFF) {
		if (mantissaBits == 0) {
			// inf
			fraction.numerator = sign;
			fraction.denominator = 0;
		} else {
			// nan
			fraction.numerator = INT_MAX;
			fraction.denominator = 0;
		}
	} else {
		int significand = mantissaBits | 1 << 23;
		int exponent = exponentBits - 127 - 23;
		if (exponent < 0) {
			fraction.numerator = sign * significand;
			fraction.denominator = 1 << (unsigned int) -exponent;
		} else {
			fraction.numerator = sign * significand * exponent;
			fraction.denominator = 1;
		}
		fraction = ifrac_reduce(fraction);
	}
	return fraction;
}

int ifrac_wholeValue(ifrac fraction) {
	return fraction.numerator / fraction.denominator;
}

int ifrac_fractionalNumerator(ifrac fraction) {
	return fraction.numerator % fraction.denominator;
}

float ifrac_floatValue(ifrac fraction) {
	return (float) fraction.numerator / (float) fraction.denominator;
}

float ifrac_floatFraction(ifrac fraction) {
	return (float) (fraction.numerator % fraction.denominator) / (float) fraction.denominator;
}

// https://en.wikipedia.org/w/index.php?title=Binary_GCD_algorithm&oldid=915604058
static unsigned int greatestCommonDivisor(unsigned int a, unsigned int b) {
	unsigned int shift = 0;
	
	if (a == 0) {
		return b;
	}
	if (b == 0) {
		return a;
	}
	
	while (((a | b) & 1) == 0) {
		shift++;
		a >>= 1;
		b >>= 1;
	}
	
	while ((a & 1) == 0) {
		a >>= 1;
	}
	
	do {
		while ((b & 1) == 0) {
			b >>= 1;
		}
		if (a > b) {
			unsigned int c = a;
			a = b;
			b = c;
		}
		b -= a;
	} while (b != 0);
	
	return a << shift;
}

ifrac ifrac_reduce(ifrac fraction) {
	unsigned int gcd = greatestCommonDivisor(abs(fraction.numerator), fraction.denominator);
	if (gcd != 0) {
		fraction.numerator /= (int) gcd;
		fraction.denominator /= gcd;
	}
	return fraction;
}

ifrac ifrac_add(ifrac lhs, ifrac rhs) {
	ifrac result;
	
	result.denominator = lhs.denominator * rhs.denominator;
	result.numerator = lhs.numerator * rhs.denominator + rhs.numerator * lhs.denominator;
	return ifrac_reduce(result);
}

ifrac ifrac_sub(ifrac lhs, ifrac rhs) {
	ifrac result;
	
	result.denominator = lhs.denominator * rhs.denominator;
	result.numerator = lhs.numerator * rhs.denominator - rhs.numerator * lhs.denominator;
	return ifrac_reduce(result);
}

ifrac ifrac_mul(ifrac lhs, ifrac rhs) {
	ifrac result;
	
	result.denominator = lhs.denominator * rhs.denominator;
	result.numerator = lhs.numerator * rhs.denominator * rhs.numerator * lhs.denominator / result.denominator;
	return ifrac_reduce(result);
}

ifrac ifrac_div(ifrac lhs, ifrac rhs) {
	ifrac result;
	
	result.denominator = lhs.denominator * rhs.numerator;
	result.numerator = lhs.numerator * rhs.denominator;
	return ifrac_reduce(result);
}

ifrac ifrac_addScalar(ifrac lhs, unsigned int rhs) {
	lhs.numerator += rhs * lhs.denominator;
	return lhs;
}

ifrac ifrac_subScalar(ifrac lhs, unsigned int rhs) {
	lhs.numerator -= rhs * lhs.denominator;
	return lhs;
}

ifrac ifrac_mulScalar(ifrac lhs, unsigned int rhs) {
	lhs.numerator *= rhs;
	return ifrac_reduce(lhs);
}

ifrac ifrac_divScalar(ifrac lhs, unsigned int rhs) {
	lhs.denominator *= rhs;
	return ifrac_reduce(lhs);
}

int ifrac_cmp(ifrac lhs, ifrac rhs) {
	uint64_t lhsNumeratorExpanded = lhs.numerator * (uint64_t) rhs.denominator;
	uint64_t rhsNumeratorExpanded = rhs.numerator * (uint64_t) lhs.denominator;
	return -(lhsNumeratorExpanded < rhsNumeratorExpanded) + (lhsNumeratorExpanded > rhsNumeratorExpanded);
}