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Subject: Re: [boost] [Review:Algorithms] Order of args to clamp
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2011-09-25 12:27:54

Dave Abrahams wrote:
> No, no, no. Sorry to be so hard-line about this, but no.

Here's a quick benchmark comparing clamp with one template type
parameter vs. three:

#include <iostream>
#include <string>

using namespace std;

#ifdef CLAMP_1_TYPE
template <typename T>
T clamp(const T& val, const T& min, const T& max)
   if (val<min) return min;
   if (val<max) return val;
   return max;

template <typename T_VAL, typename T_MIN, typename T_MAX>
T_VAL clamp(const T_VAL& val, const T_MIN& min, const T_MAX& max)
   if (val<min) return min;
   if (val<max) return val;
   return max;


int main()
   while (cin.good()) {
     string w;
     // cout << w << "\n"; // No-op version to measure i/o time
     cout << clamp<string>(w,"Aardvark","zebra") << "\n";
   return 0;

Run times reading /usr/share/dict/words and writing to /dev/null are:

No-op: 0.93
3 type clamp: 0.98
1 type clamp: 1.10

So the cost of the extra char*-to-string conversions with the 1-type
version of clamp increases the execution time of that function by more
than 3X.

Personally, I value that performance benefit above the
easier-to-describe semantics that you want.

Regards, Phil.

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