Add a FastRandomContext::randrange and use it

(cherry picked from commit 4fd2d2fc97e21efceab849576e544160fd5e3e3d)
This commit is contained in:
Pieter Wuille 2017-02-25 12:16:58 -08:00 committed by Kris Nuttycombe
parent 12d8d06c80
commit 1f41301c97
7 changed files with 73 additions and 2 deletions

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@ -685,6 +685,8 @@ AC_CHECK_DECLS([bswap_16, bswap_32, bswap_64],,,
#include <byteswap.h>
#endif])
AC_CHECK_DECLS([__builtin_clz, __builtin_clzl, __builtin_clzll])
dnl Check for MSG_NOSIGNAL
AC_MSG_CHECKING(for MSG_NOSIGNAL)
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/socket.h>]],

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@ -68,7 +68,7 @@ static void CCheckQueueSpeedPrevectorJob(benchmark::State& state)
PrevectorJob(){
}
PrevectorJob(FastRandomContext& insecure_rand){
p.resize(insecure_rand.rand32() % (PREVECTOR_SIZE*2));
p.resize(insecure_rand.randrange(PREVECTOR_SIZE*2));
}
bool operator()()
{

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@ -84,4 +84,25 @@ void static inline WriteBE64(unsigned char* ptr, uint64_t x)
memcpy(ptr, (char*)&v, 8);
}
/** Return the smallest number n such that (x >> n) == 0 (or 64 if the highest bit in x is set. */
uint64_t static inline CountBits(uint64_t x)
{
#ifdef HAVE_DECL___BUILTIN_CLZL
if (sizeof(unsigned long) >= sizeof(uint64_t)) {
return x ? 8 * sizeof(unsigned long) - __builtin_clzl(x) : 0;
}
#endif
#ifdef HAVE_DECL___BUILTIN_CLZLL
if (sizeof(unsigned long long) >= sizeof(uint64_t)) {
return x ? 8 * sizeof(unsigned long long) - __builtin_clzll(x) : 0;
}
#endif
int ret = 0;
while (x) {
x >>= 1;
++ret;
}
return ret;
}
#endif // BITCOIN_CRYPTO_COMMON_H

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@ -424,7 +424,7 @@ public:
// after addresses were pushed.
if (addr.IsValid() && !addrKnown.contains(addr.GetKey())) {
if (vAddrToSend.size() >= MAX_ADDR_TO_SEND) {
vAddrToSend[insecure_rand.rand32() % vAddrToSend.size()] = addr;
vAddrToSend[insecure_rand.randrange(vAddrToSend.size())] = addr;
} else {
vAddrToSend.push_back(addr);
}

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@ -143,6 +143,17 @@ public:
}
}
/** Generate a random integer in the range [0..range). */
uint64_t randrange(uint64_t range)
{
--range;
int bits = CountBits(range);
while (true) {
uint64_t ret = randbits(bits);
if (ret <= range) return ret;
}
}
/** Generate a random 32-bit integer. */
uint32_t rand32() { return randbits(32); }

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@ -482,4 +482,26 @@ BOOST_AUTO_TEST_CASE(chacha20_testvector)
"fab78c9");
}
BOOST_AUTO_TEST_CASE(countbits_tests)
{
FastRandomContext ctx;
for (int i = 0; i <= 64; ++i) {
if (i == 0) {
// Check handling of zero.
BOOST_CHECK_EQUAL(CountBits(0), 0);
} else if (i < 10) {
for (uint64_t j = 1 << (i - 1); (j >> i) == 0; ++j) {
// Exhaustively test up to 10 bits
BOOST_CHECK_EQUAL(CountBits(j), i);
}
} else {
for (int k = 0; k < 1000; k++) {
// Randomly test 1000 samples of each length above 10 bits.
uint64_t j = ((uint64_t)1) << (i - 1) | ctx.randbits(i - 1);
BOOST_CHECK_EQUAL(CountBits(j), i);
}
}
}
}
BOOST_AUTO_TEST_SUITE_END()

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@ -30,4 +30,19 @@ BOOST_AUTO_TEST_CASE(fastrandom_tests)
BOOST_CHECK(ctx3.rand64() != ctx4.rand64()); // extremely unlikely to be equal
}
BOOST_AUTO_TEST_CASE(fastrandom_randbits)
{
FastRandomContext ctx1;
FastRandomContext ctx2;
for (int bits = 0; bits < 63; ++bits) {
for (int j = 0; j < 1000; ++j) {
uint64_t rangebits = ctx1.randbits(bits);
BOOST_CHECK_EQUAL(rangebits >> bits, 0);
uint64_t range = ((uint64_t)1) << bits | rangebits;
uint64_t rand = ctx2.randrange(range);
BOOST_CHECK(rand < range);
}
}
}
BOOST_AUTO_TEST_SUITE_END()