wip

Author: SakiTakamachi

ext/bcmath/libbcmath/src/sqrt.c

@@ -77,19 +77,22 @@ bool bc_sqrt(bc_num *num, size_t scale)
 	if ((*num)->n_len + (rscale + 1) * 2 < sizeof(LONG_MIN_DIGITS) - 1) {
 		/* fast path */
 
-		/* Calculate the initial guess. */
-		BC_VECTOR guess_vector = 1;
-		if (num_cmp_one != BCMATH_RIGHT_GREATER) {
-			guess_vector *= bc_sqrt_get_pow_10(((*num)->n_len + rscale + 1) >> 1);
-		}
-
 		BC_VECTOR n_vector = 0;
 		size_t i = 0;
 		for (; i < (*num)->n_len + (*num)->n_scale; i++) {
 			n_vector = n_vector * BASE + (*num)->n_value[i];
 		}
 		n_vector *= bc_sqrt_get_pow_10((rscale + 1) * 2 - (*num)->n_scale);
 
+		/* Calculate the initial guess. */
+		union {
+				uint64_t i;
+				double d;
+		} u;
+		u.d = (double) n_vector;
+		u.i = (1ULL << 61) + (u.i >> 1) - (1ULL << 50);
+		BC_VECTOR guess_vector = (BC_VECTOR) u.d;
+
 		BC_VECTOR guess1_vector;
 		bool done = false;
 		while (!done) {