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Additional comments for the testing PRNG and a seeding fix. 

Rw has additional short-cycle inputs because 2^32/0x464fffff >= 2.
This commit is contained in:
Gregory Maxwell 2015-02-02 06:46:04 +00:00
parent 6efd6e7777
commit 34b898dc84
2 changed files with 8 additions and 2 deletions
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4
src/testrand.h
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@ -11,7 +11,9 @@
#include "libsecp256k1-config.h"
#endif
/** Seed the pseudorandom number generator. */
/* A non-cryptographic RNG used only for test infrastructure. */
/** Seed the pseudorandom number generator for testing. */
SECP256K1_INLINE static void secp256k1_rand_seed(uint64_t v);
/** Generate a pseudorandom 32-bit number. */

6
src/testrand_impl.h
View File

@ -18,15 +18,19 @@ SECP256K1_INLINE static void secp256k1_rand_seed(uint64_t v) {
secp256k1_Rz = v >> 32;
secp256k1_Rw = v;
/* There are two seeds with short (length 1) cycles for the Rz PRNG. */
if (secp256k1_Rz == 0 || secp256k1_Rz == 0x9068ffffU) {
secp256k1_Rz = 111;
}
if (secp256k1_Rw == 0 || secp256k1_Rw == 0x464fffffU) {
/* There are four seeds with short (length 1) cycles for the Rw PRNG. */
if (secp256k1_Rw == 0 || secp256k1_Rw == 0x464fffffU ||
secp256k1_Rw == 0x8c9ffffeU || secp256k1_Rw == 0xd2effffdU) {
secp256k1_Rw = 111;
}
}
SECP256K1_INLINE static uint32_t secp256k1_rand32(void) {
/* MWC PRNG for tests. */
secp256k1_Rz = 36969 * (secp256k1_Rz & 0xFFFF) + (secp256k1_Rz >> 16);
secp256k1_Rw = 18000 * (secp256k1_Rw & 0xFFFF) + (secp256k1_Rw >> 16);
return (secp256k1_Rw << 16) + (secp256k1_Rw >> 16) + secp256k1_Rz;