package main

/*
#include <stdlib.h>
#include <math.h>
*/

import "C"

//export CExp
func CExp(x float64) float64 {
    ret := C.exp(C.double(x))  // This result are same with result of math.Exp() on amd64/darwin.
    return float64(ret)
}

package main

import (
	"fmt"
	"math"
)

//----------------------------------------------------------------
// same with math/exp.go
func GoExp(x float64) float64 {
	const (
		Ln2Hi = 6.93147180369123816490e-01
		Ln2Lo = 1.90821492927058770002e-10
		Log2e = 1.44269504088896338700e+00

		Overflow  = 7.09782712893383973096e+02
		Underflow = -7.45133219101941108420e+02
		NearZero  = 1.0 / (1 << 28) // 2**-28
	)

	// special cases
	switch {
	case math.IsNaN(x) || math.IsInf(x, 1):
		return x
	case math.IsInf(x, -1):
		return 0
	case x > Overflow:
		return math.Inf(1)
	case x < Underflow:
		return 0
	case -NearZero < x && x < NearZero:
		return 1 + x
	}

	// reduce; computed as r = hi - lo for extra precision.
	var k int
	switch {
	case x < 0:
		k = int(Log2e*x - 0.5)
	case x > 0:
		k = int(Log2e*x + 0.5)
	}
	hi := x - float64(k)*Ln2Hi
	lo := float64(k) * Ln2Lo

	// compute
	return expmulti(hi, lo, k)
}


func expmulti(hi, lo float64, k int) float64 {
	const (
		P1 = 1.66666666666666657415e-01  /* 0x3FC55555; 0x55555555 */
		P2 = -2.77777777770155933842e-03 /* 0xBF66C16C; 0x16BEBD93 */
		P3 = 6.61375632143793436117e-05  /* 0x3F11566A; 0xAF25DE2C */
		P4 = -1.65339022054652515390e-06 /* 0xBEBBBD41; 0xC5D26BF1 */
		P5 = 4.13813679705723846039e-08  /* 0x3E663769; 0x72BEA4D0 */
	)

	r := hi - lo
	t := r * r
	c := r - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))))
	y := 1 - ((lo - (r*c)/(2-c)) - hi)
	// TODO(rsc): make sure Ldexp can handle boundary k
	return math.Ldexp(y, k)
}
//----------------------------------------------------------------

func main() {
	var a float64 = 63.5

	// C.exp()
	ret := CExp(a) * 10000.0
	fmt.Println(ret, math.Mod(ret, 100.0))

	// math.Exp() true haveArchExp
	ret = math.Exp(a) * 10000.0
	fmt.Println(ret, math.Mod(ret, 100.0))

	// math.Exp() false haveArchExp
	ret = GoExp(a) * 10000.0
	fmt.Println(ret, math.Mod(ret, 100.0))
}