1 files changed, 51 insertions, 26 deletions

diff --git a/server/src/trace.cpp b/server/src/trace.cpp
index e7c00d0..f2935a9 100644
--- a/server/src/trace.cpp
+++ b/server/src/trace.cpp
@@ -10,6 +10,26 @@ import :trace;
 
 namespace routemon::trace {
 
+class psrng
+{
+  mutable std::default_random_engine e_ = {};
+  mutable std::uniform_int_distribution<std::uint64_t> distr_ = {};
+  mutable std::mutex mut_ = {};
+
+public:
+  auto next() const -> std::uint64_t
+  {
+    auto lock = std::lock_guard{mut_};
+    return distr_(e_);
+  }
+
+  static auto instance() -> psrng const&
+  {
+    static auto const inst = psrng{};
+    return inst;
+  }
+};
+
 uuid7::uuid7()
 {
   namespace chrono = std::chrono;
@@ -23,46 +43,51 @@ uuid7::uuid7()
   if (std::countl_zero(unix_time_ms) < 16)
     throw std::runtime_error{"system time too great"};
 
-  auto rand = std::array<unsigned char, 10>{};
-  int s = RAND_bytes(rand.data(), static_cast<int>(rand.size()));
-  if (s != 1)
-  {
-    unsigned long e = ERR_get_error();
-    throw std::runtime_error{std::format(
-        "failed to generate UUID(v7): {} ({}, code {})",
-        ERR_reason_error_string(e), ERR_lib_error_string(e), e)};
-  }
+  auto const& rng = psrng::instance();
+  auto const rand1 = rng.next();
+  auto const rand2 = rng.next();
 
   auto version = std::uint64_t{0b0111};
   auto variant = std::uint64_t{0b10};
 
-  hi_ |= unix_time_ms << 16;
+  hi_ = unix_time_ms << 16;
   hi_ |= version << 12;
-  hi_ |= std::uint64_t{rand[0]} << 4;
-  hi_ |= std::uint64_t{rand[1]};
-  lo_ |= variant << 62;
-  lo_ |= std::uint64_t{rand[2]} << 54;
-  lo_ |= std::uint64_t{rand[3]} << 48;
-  lo_ |= std::uint64_t{rand[4]} << 40;
-  lo_ |= std::uint64_t{rand[5]} << 32;
-  lo_ |= std::uint64_t{rand[6]} << 24;
-  lo_ |= std::uint64_t{rand[7]} << 16;
-  lo_ |= std::uint64_t{rand[8]} << 8;
-  lo_ |= std::uint64_t{rand[9]};
+  hi_ |= rand1 & 0x0000'0000'0000'0fff;
+  lo_ = variant << 62;
+  lo_ |= rand2 >> 2;
 }
 
-auto uuid7::format(std::array<char, 37>& target) -> void
+auto uuid7::format(std::span<char, 37> target) -> void
 {
+  auto hexnibs =
+      []<std::size_t n>(std::uint64_t v, std::span<char, n> s) -> void
+  {
+    for (auto i = 0uz; i < n; i++)
+    {
+      static char const hextab[16] = {
+        '0', '1', '2', '3', '4', '5', '6', '7',
+        '8', '9', 'a', 'b', 'c', 'd', 'e', 'f',
+      };
+      s[i] = hextab[(v >> 4 * (n - 1 - i)) & 0xf];
+    }
+  };
+
   auto p____hi_hi = (hi_ & 0xffff'ffff'0000'0000) >> 32;
   auto p_hi_lo_hi = (hi_ & 0x0000'0000'ffff'0000) >> 16;
   auto p_lo_lo_hi = (hi_ & 0x0000'0000'0000'ffff) >> 0;
   auto p____hi_lo = (lo_ & 0xffff'0000'0000'0000) >> 48;
   auto p____lo_lo = (lo_ & 0x0000'ffff'ffff'ffff) >> 0;
 
-  std::format_to(
-      target.begin(), "{:0>8x}-{:0>4x}-{:0>4x}-{:0>4x}-{:0>12x}", p____hi_hi,
-      p_hi_lo_hi, p_lo_lo_hi, p____hi_lo, p____lo_lo);
-  target.back() = '\0';
+  hexnibs(p____hi_hi, target.subspan<0, 8>());
+  target[8] = '-';
+  hexnibs(p_hi_lo_hi, target.subspan<9, 4>());
+  target[13] = '-';
+  hexnibs(p_lo_lo_hi, target.subspan<14, 4>());
+  target[18] = '-';
+  hexnibs(p____hi_lo, target.subspan<19, 4>());
+  target[23] = '-';
+  hexnibs(p____lo_lo, target.subspan<24, 12>());
+  target[36] = '\0';
 }
 
 id::id() { uuid7{}.format(chars_); }