Rework NonsecureURBGBase seed sequence.

Decompose RandenPoolSeedSeq from NonsecureURBGBase.

Adjust how the RandenPoolSeedSeq detects contiguous buffers passed to the generate function. Previously it made incorrect assumptions regarding the contiguous concept, which have been replaced with some type-based tests for a small number of known contiguous random access iterator types, including raw pointers.

PiperOrigin-RevId: 452564114
Change-Id: Idab1df9dd078d8e5c565c7fa7ccb9c0d3d392ad2

1 files changed, 24 insertions, 26 deletions

diff --git a/absl/random/internal/salted_seed_seq.h b/absl/random/internal/salted_seed_seq.h
index 5953a090..06291865 100644
--- a/absl/random/internal/salted_seed_seq.h
+++ b/absl/random/internal/salted_seed_seq.h
@@ -22,6 +22,7 @@
 #include <memory>
 #include <type_traits>
 #include <utility>
+#include <vector>
 
 #include "absl/container/inlined_vector.h"
 #include "absl/meta/type_traits.h"
@@ -65,15 +66,19 @@ class SaltedSeedSeq {
 
   template <typename RandomAccessIterator>
   void generate(RandomAccessIterator begin, RandomAccessIterator end) {
+    using U = typename std::iterator_traits<RandomAccessIterator>::value_type;
+
     // The common case is that generate is called with ContiguousIterators
     // to uint arrays. Such contiguous memory regions may be optimized,
     // which we detect here.
-    using tag = absl::conditional_t<
-        (std::is_pointer<RandomAccessIterator>::value &&
-         std::is_same<absl::decay_t<decltype(*begin)>, uint32_t>::value),
+    using TagType = absl::conditional_t<
+        (std::is_same<U, uint32_t>::value &&
+         (std::is_pointer<RandomAccessIterator>::value ||
+          std::is_same<RandomAccessIterator,
+                       typename std::vector<U>::iterator>::value)),
         ContiguousAndUint32Tag, DefaultTag>;
     if (begin != end) {
-      generate_impl(begin, end, tag{});
+      generate_impl(TagType{}, begin, end, std::distance(begin, end));
     }
   }
 
@@ -89,8 +94,15 @@ class SaltedSeedSeq {
   struct DefaultTag {};
 
   // Generate which requires the iterators are contiguous pointers to uint32_t.
-  void generate_impl(uint32_t* begin, uint32_t* end, ContiguousAndUint32Tag) {
-    generate_contiguous(absl::MakeSpan(begin, end));
+  // Fills the initial seed buffer the underlying SSeq::generate() call,
+  // then mixes in the salt material.
+  template <typename Contiguous>
+  void generate_impl(ContiguousAndUint32Tag, Contiguous begin, Contiguous end,
+                     size_t n) {
+    seq_->generate(begin, end);
+    const uint32_t salt = absl::random_internal::GetSaltMaterial().value_or(0);
+    auto span = absl::Span<uint32_t>(&*begin, n);
+    MixIntoSeedMaterial(absl::MakeConstSpan(&salt, 1), span);
   }
 
   // The uncommon case for generate is that it is called with iterators over
@@ -98,27 +110,13 @@ class SaltedSeedSeq {
   // case we allocate a temporary 32-bit buffer and then copy-assign back
   // to the initial inputs.
   template <typename RandomAccessIterator>
-  void generate_impl(RandomAccessIterator begin, RandomAccessIterator end,
-                     DefaultTag) {
-    return generate_and_copy(std::distance(begin, end), begin);
-  }
-
-  // Fills the initial seed buffer the underlying SSeq::generate() call,
-  // mixing in the salt material.
-  void generate_contiguous(absl::Span<uint32_t> buffer) {
-    seq_->generate(buffer.begin(), buffer.end());
-    const uint32_t salt = absl::random_internal::GetSaltMaterial().value_or(0);
-    MixIntoSeedMaterial(absl::MakeConstSpan(&salt, 1), buffer);
-  }
-
-  // Allocates a seed buffer of `n` elements, generates the seed, then
-  // copies the result into the `out` iterator.
-  template <typename Iterator>
-  void generate_and_copy(size_t n, Iterator out) {
-    // Allocate a temporary buffer, generate, and then copy.
+  void generate_impl(DefaultTag, RandomAccessIterator begin,
+                     RandomAccessIterator, size_t n) {
+    // Allocates a seed buffer of `n` elements, generates the seed, then
+    // copies the result into the `out` iterator.
     absl::InlinedVector<uint32_t, 8> data(n, 0);
-    generate_contiguous(absl::MakeSpan(data.data(), data.size()));
-    std::copy(data.begin(), data.end(), out);
+    generate_impl(ContiguousAndUint32Tag{}, data.begin(), data.end(), n);
+    std::copy(data.begin(), data.end(), begin);
   }
 
   // Because [rand.req.seedseq] is not required to be copy-constructible,