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 DEFINE_COMPILERRT_FUNCTION(__clzdi2) 25 #ifdef __ARM_FEATURE_CLZ 26 #ifdef __ARMEB__ 27 cmp r0, 0 28 itee ne 29 clzne r0, r0 30 clzeq r0, r1 31 addeq r0, r0, 32 32 #else 33 cmp r1, 0 34 itee ne 35 clzne r0, r1 36 clzeq r0, r0 37 addeq r0, r0, 32 38 #endif 39 JMP(lr) 40 #else 41 /* Assumption: n != 0 */ 42 43 /* 44 * r0: n 45 * r1: upper half of n, overwritten after check 46 * r1: count of leading zeros in n + 1 47 * r2: scratch register for shifted r0 48 */ 49 #ifdef __ARMEB__ 50 cmp r0, 0 51 moveq r0, r1 52 #else 53 cmp r1, 0 54 movne r0, r1 55 #endif 56 movne r1, 1 57 moveq r1, 33 58 59 /* 60 * Basic block: 61 * if ((r0 >> SHIFT) == 0) 62 * r1 += SHIFT; 63 * else 64 * r0 >>= SHIFT; 65 * for descending powers of two as SHIFT. 66 */ 67 #define BLOCK(shift) \ 68 lsrs r2, r0, shift; \ 69 movne r0, r2; \ 70 addeq r1, shift \ 71 72 BLOCK(16) 73 BLOCK(8) 74 BLOCK(4) 75 BLOCK(2) 76 77 /* 78 * The basic block invariants at this point are (r0 >> 2) == 0 and 79 * r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1. 80 * 81 * r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1) 82 * ---+----------------+----------------+------------+-------------- 83 * 1 | 1 | 0 | 0 | 1 84 * 2 | 0 | 1 | -1 | 0 85 * 3 | 0 | 1 | -1 | 0 86 * 87 * The r1's initial value of 1 compensates for the 1 here. 88 */ 89 sub r0, r1, r0, lsr #1 90 91 JMP(lr) 92 #endif // __ARM_FEATURE_CLZ 93 END_COMPILERRT_FUNCTION(__clzdi2) 94
