1//===-- clzsi2.c - Implement __clzsi2 -------------------------------------===// 2// 3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4// See https://llvm.org/LICENSE.txt for license information. 5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6// 7//===----------------------------------------------------------------------===// 8// 9// This file implements count leading zeros for 32bit arguments. 10// 11//===----------------------------------------------------------------------===// 12 13#include "../assembly.h" 14 15 .syntax unified 16 .text 17 DEFINE_CODE_STATE 18 19 .p2align 2 20DEFINE_COMPILERRT_FUNCTION(__clzsi2) 21#ifdef __ARM_FEATURE_CLZ 22 clz r0, r0 23 JMP(lr) 24#else 25 // Assumption: n != 0 26 27 // r0: n 28 // r1: count of leading zeros in n + 1 29 // r2: scratch register for shifted r0 30 mov r1, 1 31 32 // Basic block: 33 // if ((r0 >> SHIFT) == 0) 34 // r1 += SHIFT; 35 // else 36 // r0 >>= SHIFT; 37 // for descending powers of two as SHIFT. 38 39#define BLOCK(shift) \ 40 lsrs r2, r0, shift; \ 41 movne r0, r2; \ 42 addeq r1, shift \ 43 44 BLOCK(16) 45 BLOCK(8) 46 BLOCK(4) 47 BLOCK(2) 48 49 // The basic block invariants at this point are (r0 >> 2) == 0 and 50 // r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1. 51 // 52 // r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1) 53 // ---+----------------+----------------+------------+-------------- 54 // 1 | 1 | 0 | 0 | 1 55 // 2 | 0 | 1 | -1 | 0 56 // 3 | 0 | 1 | -1 | 0 57 // 58 // The r1's initial value of 1 compensates for the 1 here. 59 sub r0, r1, r0, lsr #1 60 61 JMP(lr) 62#endif // __ARM_FEATURE_CLZ 63END_COMPILERRT_FUNCTION(__clzsi2) 64 65NO_EXEC_STACK_DIRECTIVE 66 67