diff options
Diffstat (limited to 'compiler-rt/lib/builtins/arm/clzdi2.S')
| -rw-r--r-- | compiler-rt/lib/builtins/arm/clzdi2.S | 72 |
1 files changed, 33 insertions, 39 deletions
diff --git a/compiler-rt/lib/builtins/arm/clzdi2.S b/compiler-rt/lib/builtins/arm/clzdi2.S index f02b98b99c8..685668b11b8 100644 --- a/compiler-rt/lib/builtins/arm/clzdi2.S +++ b/compiler-rt/lib/builtins/arm/clzdi2.S @@ -1,15 +1,15 @@ -/* ===-- clzdi2.c - Implement __clzdi2 -------------------------------------=== - * - * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. - * See https://llvm.org/LICENSE.txt for license information. - * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception - * - * ===----------------------------------------------------------------------=== - * - * This file implements count leading zeros for 64bit arguments. - * - * ===----------------------------------------------------------------------=== - */ +//===-- clzdi2.c - Implement __clzdi2 -------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file implements count leading zeros for 64bit arguments. +// +//===----------------------------------------------------------------------===// + #include "../assembly.h" .syntax unified @@ -34,14 +34,12 @@ DEFINE_COMPILERRT_FUNCTION(__clzdi2) #endif JMP(lr) #else - /* Assumption: n != 0 */ + // Assumption: n != 0 - /* - * r0: n - * r1: upper half of n, overwritten after check - * r1: count of leading zeros in n + 1 - * r2: scratch register for shifted r0 - */ + // r0: n + // r1: upper half of n, overwritten after check + // r1: count of leading zeros in n + 1 + // r2: scratch register for shifted r0 #ifdef __ARMEB__ cmp r0, 0 moveq r0, r1 @@ -52,14 +50,12 @@ DEFINE_COMPILERRT_FUNCTION(__clzdi2) movne r1, 1 moveq r1, 33 - /* - * Basic block: - * if ((r0 >> SHIFT) == 0) - * r1 += SHIFT; - * else - * r0 >>= SHIFT; - * for descending powers of two as SHIFT. - */ + // Basic block: + // if ((r0 >> SHIFT) == 0) + // r1 += SHIFT; + // else + // r0 >>= SHIFT; + // for descending powers of two as SHIFT. #define BLOCK(shift) \ lsrs r2, r0, shift; \ movne r0, r2; \ @@ -70,18 +66,16 @@ DEFINE_COMPILERRT_FUNCTION(__clzdi2) BLOCK(4) BLOCK(2) - /* - * The basic block invariants at this point are (r0 >> 2) == 0 and - * r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1. - * - * r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1) - * ---+----------------+----------------+------------+-------------- - * 1 | 1 | 0 | 0 | 1 - * 2 | 0 | 1 | -1 | 0 - * 3 | 0 | 1 | -1 | 0 - * - * The r1's initial value of 1 compensates for the 1 here. - */ + // The basic block invariants at this point are (r0 >> 2) == 0 and + // r0 != 0. This means 1 <= r0 <= 3 and 0 <= (r0 >> 1) <= 1. + // + // r0 | (r0 >> 1) == 0 | (r0 >> 1) == 1 | -(r0 >> 1) | 1 - (r0 >> 1) + // ---+----------------+----------------+------------+-------------- + // 1 | 1 | 0 | 0 | 1 + // 2 | 0 | 1 | -1 | 0 + // 3 | 0 | 1 | -1 | 0 + // + // The r1's initial value of 1 compensates for the 1 here. sub r0, r1, r0, lsr #1 JMP(lr) |
