diff options
Diffstat (limited to 'src/common/pg_prng.c')
| -rw-r--r-- | src/common/pg_prng.c | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/src/common/pg_prng.c b/src/common/pg_prng.c index c1714a02bd9..15b39411a9b 100644 --- a/src/common/pg_prng.c +++ b/src/common/pg_prng.c @@ -185,6 +185,42 @@ pg_prng_int64p(pg_prng_state *state) } /* + * Select a random int64 uniformly from the range [rmin, rmax]. + * If the range is empty, rmin is always produced. + */ +int64 +pg_prng_int64_range(pg_prng_state *state, int64 rmin, int64 rmax) +{ + int64 val; + + if (likely(rmax > rmin)) + { + uint64 uval; + + /* + * Use pg_prng_uint64_range(). Can't simply pass it rmin and rmax, + * since (uint64) rmin will be larger than (uint64) rmax if rmin < 0. + */ + uval = (uint64) rmin + + pg_prng_uint64_range(state, 0, (uint64) rmax - (uint64) rmin); + + /* + * Safely convert back to int64, avoiding implementation-defined + * behavior for values larger than PG_INT64_MAX. Modern compilers + * will reduce this to a simple assignment. + */ + if (uval > PG_INT64_MAX) + val = (int64) (uval - PG_INT64_MIN) + PG_INT64_MIN; + else + val = (int64) uval; + } + else + val = rmin; + + return val; +} + +/* * Select a random uint32 uniformly from the range [0, PG_UINT32_MAX]. */ uint32 |