llama : add floating point blue noise rng

src/llama-sampling.cpp

@@ -333,13 +333,13 @@ static void llama_sampler_top_k_impl(llama_token_data_array * cur_p, int32_t k)
     cur_p->size = k;
 }
 
-// pseudo-random number generator with ~6db/octave blue noise temporal autocorrelation
+// pseudo-random number generator with ~6db/octave blue noise
 struct blue_noise_rng {
     uint8_t  bit_depth = 0;
     uint32_t seed      = 0;
     uint32_t position  = 0;
 
-    // binary tree of 1-bit 50% duty cycle blue noise generators
+    // binary tree of 1-bit 50% duty cycle error diffusion dithering blue noise generators
     std::vector<std::array<int8_t, 2>> states; // {err0, err1} per tree node
 
     blue_noise_rng() = default;
@@ -383,11 +383,12 @@ struct blue_noise_rng {
         }
     }
 
-    uint16_t next() {
+    uint16_t next(uint32_t * hash_remainder = nullptr) {
         uint32_t h = hash(position ^ seed);
         position++;
 
-        // traverse binary tree root-to-leaf, one error diffusion ditherer per bit
+        // traverse binary tree, one error diffusion ditherer per population split
+        // thresholding output at any value still produces blue noise
         uint32_t acc = 0;
         for (int level = 0; level < bit_depth; level++) {
             auto & s = states[(1 << level) - 1 + acc]; // heap-style index
@@ -404,8 +405,31 @@ struct blue_noise_rng {
             acc = acc * 2 + out;
         }
 
+        if (hash_remainder) {
+            *hash_remainder = h >> bit_depth; // unused bits from random hash
+        }
+
         return (uint16_t)acc;
     }
+
+    // blue noise in the upper bit_depth bits, white noise hash remainder in the lower bits
+    // do not use with modulo operator, as it would just produce white noise
+    uint32_t next32() {
+        uint32_t rem;
+        uint32_t val = next(&rem);
+        return (val << (32 - bit_depth)) | rem;
+    }
+
+    // uniform double in [0, 1) with blue noise temporal autocorrelation
+    double nextf() {
+        double res = 0.0;
+        res += hash(position ^ ~seed); // fill low bits with white noise
+        res *= 1.0 / 4294967296.0;
+        res += next32();
+        res *= 1.0 / 4294967296.0;
+        if (res >= 1.0) res = std::nextafter(1.0, 0.0);
+        return res;
+    }
 };
 
 static uint32_t get_rng_seed(uint32_t seed) {