Added 32-bit and 64-bit prime_less_than_next_pow_2_or_1 functions (#5)

Author: polytypic

internals/primes/CMakeLists.txt

@@ -0,0 +1 @@
+add_conventional_executable(primes)

internals/primes/program/main.cpp

@@ -0,0 +1,76 @@
+#include <cinttypes>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <vector>
+
+//
+
+static uint64_t bit(int i) { return static_cast<uint64_t>(1) << i; }
+
+static uint64_t bits(int n) { return bit(n) * 2 - 1; }
+
+//
+
+static bool is_prime(uint64_t n) {
+  if (n <= 3)
+    return n > 1;
+  else if (n % 2 == 0 || n % 3 == 0)
+    return false;
+  else
+    for (uint64_t i = 5, m = static_cast<uint64_t>(sqrt(n) + 1); i <= m; i += 6)
+      if (n % i == 0 || n % (i + 2) == 0)
+        return false;
+  return true;
+}
+
+static std::vector<uint64_t> primes_less_than_pow_2(int m) {
+  std::vector<uint64_t> results;
+  results.reserve(64);
+  results.push_back(1);
+  for (int i = 1; i < m; ++i) {
+    uint64_t n = bits(i);
+    while (!is_prime(n))
+      n -= 2;
+    results.push_back(n);
+  }
+  return results;
+}
+
+//
+
+static void print_table(int n_bits,
+                        int keep_bits,
+                        std::vector<uint64_t> table,
+                        uint64_t de_bruijn_sequence) {
+  struct entry {
+    int i;
+    uint64_t n;
+    uint64_t v;
+  };
+
+  std::vector<entry> reindexed;
+  reindexed.resize(n_bits);
+
+  for (int i = 0; i < n_bits; ++i) {
+    uint64_t n = bits(i);
+    int j = static_cast<int>((n * de_bruijn_sequence >> (n_bits - keep_bits)) &
+                             bits(keep_bits - 1));
+    uint64_t v = table[i];
+    reindexed[j] = entry{i, n, v};
+  }
+
+  for (const auto &e : reindexed)
+    fprintf(
+        stdout, "0x%016" PRIx64 " - 0x%016" PRIx64 ", // %2d\n", e.n, e.v, e.i);
+}
+
+int main() {
+  auto primes = primes_less_than_pow_2(64);
+
+  print_table(32, 5, primes, 0x07c4acdd);
+  fprintf(stdout, "\n");
+  print_table(64, 6, primes, 0x03f08a4c6acb9dbd);
+
+  return 0;
+}

internals/CMakeLists.txt renamed to internals/tests/CMakeLists.txt

@@ -0,0 +1,39 @@
+#include "dumpster_v1/primes.hpp"
+
+#include "testing_v1/test.hpp"
+
+using namespace testing_v1;
+
+#define VERIFY_IS_PRIME_OR_1 0
+
+#if VERIFY_IS_PRIME_OR_1
+#include <cmath>
+
+static bool is_prime(uint64_t n) {
+  if (n <= 3)
+    return n > 1;
+  else if (n % 2 == 0 || n % 3 == 0)
+    return false;
+  else
+    for (uint64_t i = 5, m = static_cast<uint64_t>(sqrt(n) + 1); i <= m; i += 6)
+      if (n % i == 0 || n % (i + 2) == 0)
+        return false;
+  return true;
+}
+#endif
+
+template <class T> static void test() {
+  for (int i = 0; i < static_cast<int>(sizeof(T) * 8); ++i) {
+    T n = static_cast<T>(1) << i;
+    T p = dumpster_v1::prime_less_than_next_pow_2_or_1(n);
+#if VERIFY_IS_PRIME_OR_1
+    verify(1 == p || is_prime(p));
+#endif
+    verify(n <= p && p <= n * 2 - 1);
+  }
+}
+
+auto primes_test = test([]() {
+  test<uint32_t>();
+  test<uint64_t>();
+});

internals/testing/defaulted_test.cpp renamed to internals/tests/testing/defaulted_test.cpp

@@ -1,2 +1,2 @@
 add_conventional_library(dumpster_v1)
-target_link_libraries(dumpster_v1 INTERFACE polyfill_v1)
+target_link_libraries(dumpster_v1 PUBLIC polyfill_v1)