BLI_rand: add BLI_rng_get_char_n

Use to fill an array of bytes to random values.

3 files changed, 46 insertions, 14 deletions

diff --git a/source/blender/blenlib/BLI_rand.h b/source/blender/blenlib/BLI_rand.h
index 7b84dddcb68..f36d2faa1b8 100644
--- a/source/blender/blenlib/BLI_rand.h
+++ b/source/blender/blenlib/BLI_rand.h
@@ -49,6 +49,7 @@ void        BLI_rng_free(struct RNG *rng) ATTR_NONNULL(1);
 
 void        BLI_rng_seed(struct RNG *rng, unsigned int seed) ATTR_NONNULL(1);
 void        BLI_rng_srandom(struct RNG *rng, unsigned int seed) ATTR_NONNULL(1);
+void        BLI_rng_get_char_n(RNG *rng, char *bytes, size_t bytes_len) ATTR_NONNULL(1, 2);
 int         BLI_rng_get_int(struct RNG *rng) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL(1);
 unsigned int BLI_rng_get_uint(struct RNG *rng) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL(1);
 double      BLI_rng_get_double(struct RNG *rng) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL(1);
diff --git a/source/blender/blenlib/intern/rand.c b/source/blender/blenlib/intern/rand.c
index 66c568a7ff3..40d9a3da3d9 100644
--- a/source/blender/blenlib/intern/rand.c
+++ b/source/blender/blenlib/intern/rand.c
@@ -46,6 +46,7 @@
 
 #define MULTIPLIER  0x5DEECE66Dll
 #define MASK        0x0000FFFFFFFFFFFFll
+#define MASK_BYTES   2
 
 #define ADDEND      0xB
 #define LOWSEED     0x330E
@@ -107,6 +108,45 @@ BLI_INLINE void rng_step(RNG *rng)
 	rng->X = (MULTIPLIER * rng->X + ADDEND) & MASK;
 }
 
+void BLI_rng_get_char_n(RNG *rng, char *bytes, size_t bytes_len)
+{
+	size_t last_len = 0;
+	size_t trim_len = bytes_len;
+
+#define RAND_STRIDE (sizeof(rng->X) - MASK_BYTES)
+
+	if (trim_len > RAND_STRIDE) {
+		last_len = trim_len % RAND_STRIDE;
+		trim_len = trim_len - last_len;
+	}
+	else {
+		trim_len = 0;
+		last_len = bytes_len;
+	}
+
+	const char *data_src = (void *)&(rng->X);
+	size_t i = 0;
+	while (i != trim_len) {
+		BLI_assert(i < trim_len);
+#ifdef __BIG_ENDIAN__
+		for (size_t j = (RAND_STRIDE + MASK_BYTES) - 1; j != MASK_BYTES - 1; j--)
+#else
+		for (size_t j = 0; j != RAND_STRIDE; j++)
+#endif
+		{
+			bytes[i++] = data_src[j];
+		}
+		rng_step(rng);
+	}
+	if (last_len) {
+		for (size_t j = 0; j != last_len; j++) {
+			bytes[i++] = data_src[j];
+		}
+	}
+
+#undef RAND_STRIDE
+}
+
 int BLI_rng_get_int(RNG *rng)
 {
 	rng_step(rng);
diff --git a/tests/gtests/blenlib/BLI_array_store_test.cc b/tests/gtests/blenlib/BLI_array_store_test.cc
index 33fb454ec2f..b71dc4575f1 100644
--- a/tests/gtests/blenlib/BLI_array_store_test.cc
+++ b/tests/gtests/blenlib/BLI_array_store_test.cc
@@ -528,15 +528,6 @@ static unsigned int rand_range_i(RNG *rng, unsigned int min_i, unsigned int max_
 	return min_i + value;
 }
 
-static void rand_bytes(RNG *rng, char *data, int data_len)
-{
-	BLI_assert(data_len != 0);
-	while (data_len--) {
-		*data = BLI_rng_get_uint(rng) % 256;
-		data++;
-	}
-}
-
 static void testbuffer_list_state_random_data(
         ListBase *lb,
         const size_t stride,
@@ -548,7 +539,7 @@ static void testbuffer_list_state_random_data(
 	char *data = (char *)MEM_mallocN(data_len, __func__);
 
 	if (lb->last == NULL) {
-		rand_bytes(rng, data, data_len);
+		BLI_rng_get_char_n(rng, data, data_len);
 	}
 	else {
 		TestBuffer *tb_last = (TestBuffer *)lb->last;
@@ -557,7 +548,7 @@ static void testbuffer_list_state_random_data(
 		}
 		else {
 			memcpy(data, tb_last->data, tb_last->data_len);
-			rand_bytes(rng, &data[tb_last->data_len], data_len - tb_last->data_len);
+			BLI_rng_get_char_n(rng, &data[tb_last->data_len], data_len - tb_last->data_len);
 		}
 
 		/* perform multiple small mutations to the array. */
@@ -583,7 +574,7 @@ static void testbuffer_list_state_random_data(
 						data_len += stride;
 						data = (char *)MEM_reallocN((void *)data, data_len);
 						memmove(&data[offset + stride], &data[offset], data_len - (offset + stride));
-						rand_bytes(rng, &data[offset], stride);
+						BLI_rng_get_char_n(rng, &data[offset], stride);
 					}
 					break;
 				}
@@ -608,7 +599,7 @@ static void testbuffer_list_state_random_data(
 				{
 					if (data_len > 0) {
 						const unsigned int offset = rand_range_i(rng, 0, data_len - stride, stride);
-						rand_bytes(rng, &data[offset], stride);
+						BLI_rng_get_char_n(rng, &data[offset], stride);
 					}
 					break;
 				}
@@ -667,7 +658,7 @@ static void random_chunk_generate(
 	const size_t chunk_size_bytes = stride * chunk_count;
 	for (int i = 0; i < chunks_per_buffer; i++) {
 		char *data_chunk = (char *)MEM_mallocN(chunk_size_bytes, __func__);
-		rand_bytes(rng, data_chunk, chunk_size_bytes);
+		BLI_rng_get_char_n(rng, data_chunk, chunk_size_bytes);
 		testchunk_list_add(lb, data_chunk, chunk_size_bytes);
 	}
 	BLI_rng_free(rng);