Fix for 32-bit Windows

Author: bzoz

src/hdr_histogram.c

@@ -90,14 +90,32 @@ static int64_t power(int64_t base, int64_t exp)
 }
 
 #if defined(_MSC_VER)
-#pragma intrinsic(_BitScanReverse64)
+#   if defined(_WIN64)
+#       pragma intrinsic(_BitScanReverse64)
+#   else
+#       pragma intrinsic(_BitScanReverse)
+#   endif 
 #endif
 
 static int32_t get_bucket_index(const struct hdr_histogram* h, int64_t value)
 {
 #if defined(_MSC_VER)
     uint32_t leading_zero = 0;
-	_BitScanReverse64(&leading_zero, value | h->sub_bucket_mask);
+    int64_t masked_value = value | h->sub_bucket_mask;
+#   if defined(_WIN64)
+        _BitScanReverse64(&leading_zero, masked_value);
+#   else
+        uint32_t high = masked_value >> 32;
+        if  (_BitScanReverse(&leading_zero, high))
+        {
+            leading_zero += 32;
+        }
+        else
+        {
+            uint32_t low = masked_value & 0x00000000FFFFFFFF;
+            _BitScanReverse(&leading_zero, low);
+        }
+#   endif
 	int32_t pow2ceiling = 64 - (63 - leading_zero); // smallest power of 2 containing value
 #else
     int32_t pow2ceiling = 64 - __builtin_clzll(value | h->sub_bucket_mask); // smallest power of 2 containing value