We need the Intel intrinsic.

lemire · lemire · commit b5a2c4104911 · 2019-01-16T13:13:03.000-05:00
diff --git a/include/simdjson/portability.h b/include/simdjson/portability.h
@@ -54,7 +54,7 @@ static inline bool mul_overflow(uint64_t  value1, uint64_t  value2, uint64_t *re
 
 /* result might be undefined when input_num is zero */
 static inline int trailingzeroes(uint64_t input_num) {
-	return __builtin_ctzll(input_num); // for some reason, the Intel intrinsic _tzcnt_u64 may be missing
+	return _tzcnt_u64(input_num); // for some reason, the Intel intrinsic _tzcnt_u64 may be missing
 }
 
 /* result might be undefined when input_num is zero */

Original file line number	Diff line number	Diff line change
`@@ -54,7 +54,7 @@ static inline bool mul_overflow(uint64_t value1, uint64_t value2, uint64_t *re`
`54`	`54`
`55`	`55`	`/* result might be undefined when input_num is zero */`
`56`	`56`	`static inline int trailingzeroes(uint64_t input_num) {`
`57`		`- return __builtin_ctzll(input_num); // for some reason, the Intel intrinsic _tzcnt_u64 may be missing`
	`57`	`+ return _tzcnt_u64(input_num); // for some reason, the Intel intrinsic _tzcnt_u64 may be missing`
`58`	`58`	`}`
`59`	`59`
`60`	`60`	`/* result might be undefined when input_num is zero */`