1 /* ===-- clzdi2.c - Implement __clzdi2 -------------------------------------===
3 * The LLVM Compiler Infrastructure
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
8 * ===----------------------------------------------------------------------===
10 * This file implements count leading zeros for 64bit arguments.
12 * ===----------------------------------------------------------------------===
14 #include "../assembly.h"
21 DEFINE_COMPILERRT_FUNCTION(__clzdi2)
22 #ifdef __ARM_FEATURE_CLZ
38 /* Assumption: n != 0 */
42 * r1: upper half of n, overwritten after check
43 * r1: count of leading zeros in n + 1
44 * r2: scratch register for shifted r0
58 * if ((r0 >> SHIFT) == 0)
62 * for descending powers of two as SHIFT.
64 #define BLOCK(shift) \
75 * The basic block invariants at this point are (r0 >> 2) == 0 and
76 * r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1.
78 * r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1)
79 * ---+----------------+----------------+------------+--------------
84 * The r1's initial value of 1 compensates for the 1 here.
86 sub r0, r1, r0, lsr #1
89 #endif // __ARM_FEATURE_CLZ
90 END_COMPILERRT_FUNCTION(__clzdi2)
92 NO_EXEC_STACK_DIRECTIVE