Riff Container Stream Writing (#1116)

* * Added option to get random bytes from RandomGenerator
* Added ability to allocate only in current block on MemoryArena
* Allowed RiffContainer to not allocate new Data blocks, if can just extend the Data it has (because it's at the end of current block and there is space for the new data).
* Added coverage for change on Riff unit test

* Add test coverage for allocations over multiple Data blocks.

* Improve comment on riff unit tests.

1 files changed, 78 insertions, 0 deletions

diff --git a/source/core/slang-random-generator.cpp b/source/core/slang-random-generator.cpp
index ce43067aa..ec06336f1 100644
--- a/source/core/slang-random-generator.cpp
+++ b/source/core/slang-random-generator.cpp
@@ -71,6 +71,57 @@ int64_t RandomGenerator::nextInt64InRange(int64_t min, int64_t max)
     return (nextPositiveInt64() % diff) + min;
 }
 
+static uint8_t* _nextData(RandomGenerator* rand, uint8_t* out, size_t size)
+{
+    if (size)
+    {
+        SLANG_ASSERT(size <= 4);
+        uint32_t v = uint32_t(rand->nextInt32());
+        uint8_t* dst = (uint8_t*)out;
+        for (size_t i = 0; i < size; ++i)
+        {
+            dst[i] = uint8_t(v);
+            v >>= 8;
+        }
+    }
+    return out + size;
+}
+
+void RandomGenerator::nextData(void* out, size_t size)
+{
+    uint8_t* dst = (uint8_t*)out;
+    uint8_t*const end = dst + size;
+
+    // For short runs just output
+    if (size <= 4)
+    {
+        _nextData(this, dst, size);
+        return;
+    }
+    
+    {
+        const size_t preAlign = size_t(((size_t(dst) + 3) & ~size_t(3)) - size_t(dst));
+        dst = _nextData(this, dst, preAlign);
+    }
+
+    // Check invariants
+    SLANG_ASSERT((size_t(dst) & 3) == 0 && end >= dst);
+
+    {
+        const size_t middleCount = size_t(end - dst) >> 2;
+        if (middleCount)
+        {
+            nextInt32s((int32_t*)dst, middleCount);
+            dst += middleCount * sizeof(int32_t);
+        }
+    }
+
+    // Check invariants
+    SLANG_ASSERT((size_t(dst) & 3) == 0 && end >= dst);
+
+    _nextData(this, dst, size_t(end - dst));
+}
+
 /* static */RandomGenerator* RandomGenerator::create(int32_t seed)
 {
     return new DefaultRandomGenerator(seed);
@@ -155,7 +206,34 @@ int32_t Mt19937RandomGenerator::nextInt32()
     return int32_t(y);
 }
 
+void Mt19937RandomGenerator::nextInt32s(int32_t* dst, size_t count)
+{
+    while (count)
+    {
+        if (m_index >= kNumEntries)
+        {
+            _generate();
+        }
+
+        const size_t remaining = kNumEntries - m_index;
+        const size_t run = (count < remaining) ? count : remaining;
+
+        const uint32_t* src = m_mt + m_index;
+        for (size_t i = 0; i < run; i++)
+        {
+            uint32_t y = src[i];
+            y = y ^ (y >> 11);
+            y = y ^ ((y << 7) & uint32_t(0x9d2c5680u));
+            y = y ^ ((y << 15) & uint32_t(0xefc6000u));
+            y = y ^ (y >> 18);
 
+            dst[i] = int32_t(y);
+        }
 
+        m_index += int(run);
+        dst += run;
+        count -= run;
+    }
+}
 
 } // namespace Slang