Author: Álvaro Begué
Date: 16:12:36 07/20/04
Go up one level in this thread
By keeping several different max_value variables, you can break the dependency
chain between iterations of the loop.
int find_max_original(int const *values){
int max_value = 0, i;
for (i=0; i<= 99; i++) {
if (values[i] > max_value) max_value = values[i];
}
return max_value;
}
int find_max_faster(int const *values){
int max_value_0=values[0];
int max_value_1=values[1];
int max_value_2=values[2];
int max_value_3=values[3];
int const *end = values+100;
for(values+=4;values!=end;values+=4){
if(max_value_0<values[0])
max_value_0=values[0];
if(max_value_1<values[1])
max_value_1=values[1];
if(max_value_2<values[2])
max_value_2=values[2];
if(max_value_3<values[3])
max_value_3=values[3];
}
if(max_value_0<max_value_1)
max_value_0=max_value_1;
if(max_value_2<max_value_3)
max_value_2=max_value_3;
if(max_value_0<max_value_2)
max_value_0=max_value_2;
return max_value_0;
}
find_max_faster() is more than twice as fast as find_max_original(). I'm using
gcc 3.4.0 with options -O3 and -mpentium4.
Can other people, please, test it with other compilers?
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