util: move MapIntoRange() for reuse in fuzz tests

Author: fanquake

src/blockfilter.cpp

@@ -24,37 +24,6 @@ static const std::map<BlockFilterType, std::string> g_filter_types = {
     {BlockFilterType::BASIC, "basic"},
 };
 
-// Map a value x that is uniformly distributed in the range [0, 2^64) to a
-// value uniformly distributed in [0, n) by returning the upper 64 bits of
-// x * n.
-//
-// See: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
-static uint64_t MapIntoRange(uint64_t x, uint64_t n)
-{
-#ifdef __SIZEOF_INT128__
-    return (static_cast<unsigned __int128>(x) * static_cast<unsigned __int128>(n)) >> 64;
-#else
-    // To perform the calculation on 64-bit numbers without losing the
-    // result to overflow, split the numbers into the most significant and
-    // least significant 32 bits and perform multiplication piece-wise.
-    //
-    // See: https://stackoverflow.com/a/26855440
-    uint64_t x_hi = x >> 32;
-    uint64_t x_lo = x & 0xFFFFFFFF;
-    uint64_t n_hi = n >> 32;
-    uint64_t n_lo = n & 0xFFFFFFFF;
-
-    uint64_t ac = x_hi * n_hi;
-    uint64_t ad = x_hi * n_lo;
-    uint64_t bc = x_lo * n_hi;
-    uint64_t bd = x_lo * n_lo;
-
-    uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
-    uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
-    return upper64;
-#endif
-}
-
 uint64_t GCSFilter::HashToRange(const Element& element) const
 {
     uint64_t hash = CSipHasher(m_params.m_siphash_k0, m_params.m_siphash_k1)

src/test/fuzz/golomb_rice.cpp

@@ -19,20 +19,6 @@
 #include <vector>
 
 namespace {
-uint64_t MapIntoRange(const uint64_t x, const uint64_t n)
-{
-    const uint64_t x_hi = x >> 32;
-    const uint64_t x_lo = x & 0xFFFFFFFF;
-    const uint64_t n_hi = n >> 32;
-    const uint64_t n_lo = n & 0xFFFFFFFF;
-    const uint64_t ac = x_hi * n_hi;
-    const uint64_t ad = x_hi * n_lo;
-    const uint64_t bc = x_lo * n_hi;
-    const uint64_t bd = x_lo * n_lo;
-    const uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
-    const uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
-    return upper64;
-}
 
 uint64_t HashToRange(const std::vector<uint8_t>& element, const uint64_t f)
 {

src/util/golombrice.h

@@ -40,4 +40,35 @@ uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P)
     return (q << P) + r;
 }
 
+// Map a value x that is uniformly distributed in the range [0, 2^64) to a
+// value uniformly distributed in [0, n) by returning the upper 64 bits of
+// x * n.
+//
+// See: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+static inline uint64_t MapIntoRange(uint64_t x, uint64_t n)
+{
+#ifdef __SIZEOF_INT128__
+    return (static_cast<unsigned __int128>(x) * static_cast<unsigned __int128>(n)) >> 64;
+#else
+    // To perform the calculation on 64-bit numbers without losing the
+    // result to overflow, split the numbers into the most significant and
+    // least significant 32 bits and perform multiplication piece-wise.
+    //
+    // See: https://stackoverflow.com/a/26855440
+    const uint64_t x_hi = x >> 32;
+    const uint64_t x_lo = x & 0xFFFFFFFF;
+    const uint64_t n_hi = n >> 32;
+    const uint64_t n_lo = n & 0xFFFFFFFF;
+
+    const uint64_t ac = x_hi * n_hi;
+    const uint64_t ad = x_hi * n_lo;
+    const uint64_t bc = x_lo * n_hi;
+    const uint64_t bd = x_lo * n_lo;
+
+    const uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF);
+    const uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32);
+    return upper64;
+#endif
+}
+
 #endif // BITCOIN_UTIL_GOLOMBRICE_H