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random: add RandomMixin::randbits with compile-known bits

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In many cases, it is known at compile time how many bits are requested from
randbits. Provide a variant of randbits that accepts this number as a template,
to make sure the compiler can make use of this knowledge. This is used immediately
in rand32() and randbool(), and a few further call sites.
This commit is contained in:
Pieter Wuille
2024-03-10 12:38:14 -04:00
parent 21ce9d8658
commit ddb7d26cfd
6 changed files with 52 additions and 9 deletions
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6
src/test/crypto_tests.cpp
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@@ -1195,7 +1195,7 @@ BOOST_AUTO_TEST_CASE(muhash_tests)
uint256 res;
int table[4];
for (int i = 0; i < 4; ++i) {
table[i] = g_insecure_rand_ctx.randbits(3);
table[i] = g_insecure_rand_ctx.randbits<3>();
}
for (int order = 0; order < 4; ++order) {
MuHash3072 acc;
@@ -1215,8 +1215,8 @@ BOOST_AUTO_TEST_CASE(muhash_tests)
}
}
MuHash3072 x = FromInt(g_insecure_rand_ctx.randbits(4)); // x=X
MuHash3072 y = FromInt(g_insecure_rand_ctx.randbits(4)); // x=X, y=Y
MuHash3072 x = FromInt(g_insecure_rand_ctx.randbits<4>()); // x=X
MuHash3072 y = FromInt(g_insecure_rand_ctx.randbits<4>()); // x=X, y=Y
MuHash3072 z; // x=X, y=Y, z=1
z *= x; // x=X, y=Y, z=X
z *= y; // x=X, y=Y, z=X*Y

22
src/test/random_tests.cpp
View File

@@ -107,7 +107,7 @@ BOOST_AUTO_TEST_CASE(fastrandom_randbits)
BOOST_AUTO_TEST_CASE(randbits_test)
{
FastRandomContext ctx_lens; //!< RNG for producing the lengths requested from ctx_test.
FastRandomContext ctx_test; //!< The RNG being tested.
FastRandomContext ctx_test1(true), ctx_test2(true); //!< The RNGs being tested.
int ctx_test_bitsleft{0}; //!< (Assumed value of) ctx_test::bitbuf_len
// Run the entire test 5 times.
@@ -122,7 +122,25 @@ BOOST_AUTO_TEST_CASE(randbits_test)
// Decide on a number of bits to request (0 through 64, inclusive; don't use randbits/randrange).
int bits = ctx_lens.rand64() % 65;
// Generate that many bits.
uint64_t gen = ctx_test.randbits(bits);
uint64_t gen = ctx_test1.randbits(bits);
// For certain bits counts, also test randbits<Bits> and compare.
uint64_t gen2;
if (bits == 0) {
gen2 = ctx_test2.randbits<0>();
} else if (bits == 1) {
gen2 = ctx_test2.randbits<1>();
} else if (bits == 7) {
gen2 = ctx_test2.randbits<7>();
} else if (bits == 32) {
gen2 = ctx_test2.randbits<32>();
} else if (bits == 51) {
gen2 = ctx_test2.randbits<51>();
} else if (bits == 64) {
gen2 = ctx_test2.randbits<64>();
} else {
gen2 = ctx_test2.randbits(bits);
}
BOOST_CHECK_EQUAL(gen, gen2);
// Make sure the result is in range.
if (bits < 64) BOOST_CHECK_EQUAL(gen >> bits, 0);
// Mark all the seen bits in the output.