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标题:
为什么 C++ 只比 VBA 快 4倍？
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作者:
蕾欧娜
时间:
2015-4-20 10:09
标题:
为什么 C++ 只比 VBA 快 4倍？
用C++和VBA分别写了一段用随机数字测试
的值的算法，用500万个随机数，发现VBA需要570毫秒，而C++则需要150毫秒。这也太让人失望了把，C++写起来那么麻烦，起码也要快个几个数量级吧？python就更别说了，居然要7秒钟。求各位大神帮我看看是不是我的代码没优化好？
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（平台是Visual Studio，已经开了Release模式）
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计算方法：生成
,
两个在0 到
之间的随机数，数一数这些数字里面有多少个落在了半径为
的1/4圆的扇形里面，用这个数字代表扇形面积，用总随机数数量代表正方形面积。因为扇形的面积是
,而正方形的面积是
, 可得知
=扇形面积/正方形面积 * 4
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C++代码：
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#include "stdafx.h"
#include <iostream>
#include <time.h>
using namespace std;
void
main(){
double
st = clock();
double
rand_max =
32767
; srand((
int
)time(
0
));
unsigned
int
simulate_total =
2500000
;
unsigned
int
inside_count =
0
;
unsigned
int
radius = rand_max * rand_max;
unsigned
int
randA;
unsigned
int
randB;
unsigned
int
randA_opp;
unsigned
int
randB_opp; for (
unsigned
int
i =
1
; i < simulate_total; i++){ randA = rand(); randB = rand(); if ((randA * randA + randB * randB) < radius){ inside_count++; } randA_opp = rand_max - randA; randB_opp = rand_max - randB; if ((randA_opp * randA_opp + randB_opp * randB_opp) < radius){ inside_count++; } } cout << inside_count /
double
(simulate_total) *
2
<< endl; cout << clock() - st << endl;}
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VBA代码:
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Sub
simulate_pi
()Dim area_count As
Double
: area_count =
0
Dim simulate_count As
Double
: simulate_count =
2500000
Dim i As
Double
Dim randA As
Double
, randB As
Double
Dim randA_opp As
Double
, randB_opp As
Double
For i =
1
To simulate_count randA = Math.Rnd() randB = Math.Rnd() randA_opp =
1
- randA randB_opp =
1
- randB If randA * randA + randB * randB <
1
Then area_count = area_count +
1
End If If randA_opp * randA_opp + randB_opp * randB_opp <
1
Then area_count = area_count +
1
End IfNext iDebug.Print
"Estimate: "
, area_count / simulate_count *
2
End Sub
'VBA内测时间的方法：
'新建一个module，把以下代码复制进去，然后运行test.
Option ExplicitPrivate Declare Function
getFrequency
Lib
"kernel32"
_Alias
"QueryPerformanceFrequency"
(cyFrequency As Currency) As
Long
Private Declare Function
getTickCount
Lib
"kernel32"
_Alias
"QueryPerformanceCounter"
(cyTickCount As Currency) As
Long
'
Function
MicroTimer
() As
Double
'
' Returns seconds.
'
Dim cyTicks1 As Currency Static cyFrequency As Currency
'
MicroTimer =
0
' Get frequency.
If cyFrequency =
0
Then getFrequency cyFrequency
' Get ticks.
getTickCount cyTicks1
' Seconds
If cyFrequency Then MicroTimer = cyTicks1 / cyFrequencyEnd FunctionSub
test
() Dim st: st = MicroTimer Call simulate_pi Debug.Print (MicroTimer - st) *
1000
End Sub
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Python代码:
#!/usr/bin/python
# Filename : pi_simulate.py
import
random
import
time
time_start = time.perf_counter()inside_count =
0
simulate_total =
2500000
randA =
0
randB =
0
for i in
range
(
1
, simulate_total): randA = random.uniform(
0
,
1
) randB = random.uniform(
0
,
1
) if ((randA * randA + randB * randB) <
1
): inside_count = inside_count +
1
randA_opp =
1
- randA randB_opp =
1
- randB if ((randA_opp * randA_opp + randB_opp * randB_opp) <
1
): inside_count = inside_count +
1
print (inside_count/simulate_total*
2
)print (
"Time spent"
, time.perf_counter() - time_start)
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