What is the fastest search method for a sorted array?

Question

Answering to another question, I wrote the program below to compare different search methods in a sorted array. Basically I compared two implementations of Interpolation search

Answer 1

Benchmarked on Win32 Core2 Quad Q6600, gcc v4.3 msys. Compiling with g++ -O3, nothing fancy.

Observation - the asserts, timing and loop overhead is about 40%, so any gains listed below should be divided by 0.6 to get the actual improvement in the algorithms under test.

Simple answers:

1. On my machine replacing the int64_t with int for "low", "high" and "mid" in interpolationSearch gives a 20% to 40% speed up. This is the fastest easy method I could find. It is taking about 150 cycles per look-up on my machine (for the array size of 100000). That's roughly the same number of cycles as a cache miss. So in real applications, looking after your cache is probably going to be the biggest factor.

2. Replacing binarySearch's "/2" with a ">>1" gives a 4% speed up.

3. Using STL's binary_search algorithm, on a vector containing the same data as "arr", is about the same speed as the hand coded binarySearch. Although on the smaller "size"s STL is much slower - around 40%.