/*
  丸め方向による計算結果の違い（Linux / FreeBSD 3.x用）
	Written by Takeshi OGITA.	2000/12/4
*/

#include <stdio.h>
#include <fpu_control.h>

#define Near _FPU_SETCW(cwnear) /* 最近点への丸め */
#define Up   _FPU_SETCW(cwup)   /* 上への丸め */
#define Down _FPU_SETCW(cwdown) /* 下への丸め */
#define Chop _FPU_SETCW(cwchop) /* 切捨て */

fpu_control_t cwnear = _FPU_RC_NEAREST | _FPU_IEEE;
fpu_control_t cwup   = _FPU_RC_UP      | _FPU_IEEE;
fpu_control_t cwdown = _FPU_RC_DOWN    | _FPU_IEEE;
fpu_control_t cwchop = _FPU_RC_ZERO    | _FPU_IEEE;


#define ND 100

int main()
{
	int i, ii, n;
	double prod;
	double A[ND], B[ND], X[ND], Y[ND];

	n = ND;

	ii = 1;
	for(i=0; i<n; i++){
		ii *= -1;
		X[i] = 1.0*i;
		Y[i] = 1.0*ii;
	}

	/* 最近点への丸め */
	Near;
	for(i=0; i<n; i++){
		A[i] = X[i]/10.0;
		B[i] = Y[i]/10.0;
	}
	prod = 0.0;
	for(i=0; i<n; i++) prod += A[i]*B[i];
	printf("inner product (Near) = %25.20f\n", prod);

	/* 上への丸め */
	Up;
	for(i=0; i<n; i++){
		A[i] = X[i]/10.0;
		B[i] = Y[i]/10.0;
	}
	prod = 0.0;
	for(i=0; i<n; i++) prod += A[i]*B[i];
	printf("inner product (Up)   = %25.20f\n", prod);

	/* 下への丸め */
	Down;
	for(i=0; i<n; i++){
		A[i] = X[i]/10.0;
		B[i] = Y[i]/10.0;
	}
	prod = 0.0;
	for(i=0; i<n; i++) prod += A[i]*B[i];
	printf("inner product (Down) = %25.20f\n", prod);

	/* 切捨て */
	Chop;
	for(i=0; i<n; i++){
		A[i] = X[i]/10.0;
		B[i] = Y[i]/10.0;
	}
	prod = 0.0;
	for(i=0; i<n; i++) prod += A[i]*B[i];
	printf("inner product (Chop) = %25.20f\n", prod);

	return 0;
}
/*
=====================================================================

＜実行結果＞
inner product (Near) =    0.50000000000000000000
inner product (Up)   =    0.50000000000000344169
inner product (Down) =    0.49999999999999650280
inner product (Chop) =    0.49999999999999994449
*/