1/* ===-- clzdi2.c - Implement __clzdi2 -------------------------------------=== 2 * 3 * The LLVM Compiler Infrastructure 4 * 5 * This file is dual licensed under the MIT and the University of Illinois Open 6 * Source Licenses. See LICENSE.TXT for details. 7 * 8 * ===----------------------------------------------------------------------=== 9 * 10 * This file implements count leading zeros for 64bit arguments. 11 * 12 * ===----------------------------------------------------------------------=== 13 */ 14#include "../assembly.h" 15 16 .syntax unified 17 .text 18#if __ARM_ARCH_ISA_THUMB == 2 19 .thumb 20#endif 21 22 23 .p2align 2 24#if __ARM_ARCH_ISA_THUMB == 2 25DEFINE_COMPILERRT_THUMB_FUNCTION(__clzdi2) 26#else 27DEFINE_COMPILERRT_FUNCTION(__clzdi2) 28#endif 29#ifdef __ARM_FEATURE_CLZ 30#ifdef __ARMEB__ 31 cmp r0, 0 32 itee ne 33 clzne r0, r0 34 clzeq r0, r1 35 addeq r0, r0, 32 36#else 37 cmp r1, 0 38 itee ne 39 clzne r0, r1 40 clzeq r0, r0 41 addeq r0, r0, 32 42#endif 43 JMP(lr) 44#else 45 /* Assumption: n != 0 */ 46 47 /* 48 * r0: n 49 * r1: upper half of n, overwritten after check 50 * r1: count of leading zeros in n + 1 51 * r2: scratch register for shifted r0 52 */ 53#ifdef __ARMEB__ 54 cmp r0, 0 55 moveq r0, r1 56#else 57 cmp r1, 0 58 movne r0, r1 59#endif 60 movne r1, 1 61 moveq r1, 33 62 63 /* 64 * Basic block: 65 * if ((r0 >> SHIFT) == 0) 66 * r1 += SHIFT; 67 * else 68 * r0 >>= SHIFT; 69 * for descending powers of two as SHIFT. 70 */ 71#define BLOCK(shift) \ 72 lsrs r2, r0, shift; \ 73 movne r0, r2; \ 74 addeq r1, shift \ 75 76 BLOCK(16) 77 BLOCK(8) 78 BLOCK(4) 79 BLOCK(2) 80 81 /* 82 * The basic block invariants at this point are (r0 >> 2) == 0 and 83 * r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1. 84 * 85 * r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1) 86 * ---+----------------+----------------+------------+-------------- 87 * 1 | 1 | 0 | 0 | 1 88 * 2 | 0 | 1 | -1 | 0 89 * 3 | 0 | 1 | -1 | 0 90 * 91 * The r1's initial value of 1 compensates for the 1 here. 92 */ 93 sub r0, r1, r0, lsr #1 94 95 JMP(lr) 96#endif // __ARM_FEATURE_CLZ 97END_COMPILERRT_FUNCTION(__clzdi2) 98