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High performance wrapper for CSPRNG arc4random(3)

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$begingroup$

This function is a wrapper for arc4random(3), a cryptographic pseudo-random number generator on macOS and BSDs, but you can also get it by installing libbsd-devel on most Linux distros.

It serves the same purpose as arc4random_uniform(3), the official wrapper for arc4random(3), i.e. to generate a nonnegative random integer less than range.

static inline unsigned random_uniform(unsigned range) 
 static uint32_t random_32b;
 static uint32_t full_32b;

 if (full_32b < range) 
 random_32b = arc4random();
 full_32b = UINT32_MAX;
 

 unsigned result = random_32b % range;
 random_32b /= range;
 full_32b /= range;

 return result;

You can find the implementation of arc4random_uniform(3) on macOS at the bottom of this page. Basically, it makes use of the rejection method to produce uniform deviates and eliminate the modulo bias. On the other hand, my implementation tries to eliminate the modulo bias by keeping track of the maximum possible range of the remaining random bytes in full_32b. What's more, it saves the unused random bytes in a static variable for future use, as a call to arc4random(3) can be costly. It appears to be faster according to my benchmark, but I'm not sure if it's correct.

performance beginner c random cryptography

share|improve this question

edited 5 mins ago

nalzok

asked 10 mins ago

nalzoknalzok

286212

$endgroup$

add a comment | 

0

$begingroup$

This function is a wrapper for arc4random(3), a cryptographic pseudo-random number generator on macOS and BSDs, but you can also get it by installing libbsd-devel on most Linux distros.

It serves the same purpose as arc4random_uniform(3), the official wrapper for arc4random(3), i.e. to generate a nonnegative random integer less than range.

static inline unsigned random_uniform(unsigned range) 
 static uint32_t random_32b;
 static uint32_t full_32b;

 if (full_32b < range) 
 random_32b = arc4random();
 full_32b = UINT32_MAX;
 

 unsigned result = random_32b % range;
 random_32b /= range;
 full_32b /= range;

 return result;

You can find the implementation of arc4random_uniform(3) on macOS at the bottom of this page. Basically, it makes use of the rejection method to produce uniform deviates and eliminate the modulo bias. On the other hand, my implementation tries to eliminate the modulo bias by keeping track of the maximum possible range of the remaining random bytes in full_32b. What's more, it saves the unused random bytes in a static variable for future use, as a call to arc4random(3) can be costly. It appears to be faster according to my benchmark, but I'm not sure if it's correct.

performance beginner c random cryptography

share|improve this question

edited 5 mins ago

nalzok

asked 10 mins ago

nalzoknalzok

286212

$endgroup$

add a comment | 

$begingroup$

This function is a wrapper for arc4random(3), a cryptographic pseudo-random number generator on macOS and BSDs, but you can also get it by installing libbsd-devel on most Linux distros.

It serves the same purpose as arc4random_uniform(3), the official wrapper for arc4random(3), i.e. to generate a nonnegative random integer less than range.

static inline unsigned random_uniform(unsigned range) 
 static uint32_t random_32b;
 static uint32_t full_32b;

 if (full_32b < range) 
 random_32b = arc4random();
 full_32b = UINT32_MAX;
 

 unsigned result = random_32b % range;
 random_32b /= range;
 full_32b /= range;

 return result;

You can find the implementation of arc4random_uniform(3) on macOS at the bottom of this page. Basically, it makes use of the rejection method to produce uniform deviates and eliminate the modulo bias. On the other hand, my implementation tries to eliminate the modulo bias by keeping track of the maximum possible range of the remaining random bytes in full_32b. What's more, it saves the unused random bytes in a static variable for future use, as a call to arc4random(3) can be costly. It appears to be faster according to my benchmark, but I'm not sure if it's correct.

performance beginner c random cryptography

share|improve this question

edited 5 mins ago

nalzok

asked 10 mins ago

nalzoknalzok

286212

$endgroup$

static inline unsigned random_uniform(unsigned range) 
 static uint32_t random_32b;
 static uint32_t full_32b;

 if (full_32b < range) 
 random_32b = arc4random();
 full_32b = UINT32_MAX;
 

 unsigned result = random_32b % range;
 random_32b /= range;
 full_32b /= range;

 return result;

share|improve this question

edited 5 mins ago

nalzok

asked 10 mins ago

nalzoknalzok

286212

share|improve this question

edited 5 mins ago

nalzok

asked 10 mins ago

nalzoknalzok

286212

asked 10 mins ago

nalzoknalzok

286212

asked 10 mins ago

nalzoknalzok

286212