#include "mtl/target.hpp"

#include "mtl/fixed.hpp"

TARGET_ARM_MODE

namespace mtl {

fixed fixed::operator/(fixed rhs) const {
	int32_t raw_result;
	asm(
			// This division implementation has two methods it can use.
			// The fastest uses a left shift followed by a single division. The value is shifted
			// first to preserve the decimal part. Unfortunately, this means large numerators
			// will cause the operation to overflow. In this case, a compatible method will be
			// used. This method uses two divisions, one to calculate the integral quotient,
			// and one to calculate the decimal part. Both these methods work for negative numbers as well.
			".arm;"
			"movs	r1, %[d];"            // Load numerator and denominator, and check if negative or zero
			"beq	4f;"
			"movs	r0, %[n];"
			"blt	1f;"
			"tst	r0, #0x7e000000;"     // Check if the numerator is large enough to overflow
			"bne	3f;"
			"b	2f;"
			"1:"	// check_negative
			"mvn	r2, r0;"              // Check if the numerator is large enough to overflow.
			"tst	r2, #0x7e000000;"
			"bne	3f;"
			"2:"	// fast_div           // Fast method
			"lsl	r0, #6;"              // Shift first to avoid truncation
			"swi	#0x60000;"            // GBA Div syscall
			"mov	%[res], r0;"
			"b	5f;"
			"3:"	// compat_div         // Compatible method
			"swi	#0x60000;"            // Compute quotient and shift
			"lsl	r2, r0, #6;" 
			"mov	r0, r1;"              // Div syscall puts the modulus in r1, use it as the numerator
			"lsr	r1, %[d], #6;"        // Load the denominator again, shifted right to calculate decimal part
			"swi	#0x60000;"
			"mov	%[res], r2;"          // Calculate the final result
			"add	%[res], r0;"
			"b	5f;"
			"4:"	// zero_div
			"teq	%[n], %[d];"          // Set result to largest possible negative/positive value.
			"movmi	%[res], #0x80000000;"
			"movpl	%[res], #0x7FFFFFFF;"
			"5:"
			: [res] "=r" (raw_result)
			: [n] "r" (x),
			[d] "r" (rhs.x)
			   :  "r0", "r1", "r2", "r3"
				   );
	return from_raw(raw_result);
}

} // namespace mtl

TARGET_END_MODE