问题描述
我有一个位数组实现，其中第 0 个索引是数组中第一个字节的 MSB，第 8 个索引是第二个字节的 MSB，等等......
I have a bit array implementation where the 0th index is the MSB of the first byte in an array, the 8th index is the MSB of the second byte, etc...
找到在这个位数组中设置的第一位的快速方法是什么?我查找的所有相关解决方案都找到了第一个最不重要的位，但我需要第一个最重要的位.所以，给定 0x00A1，我想要 8(因为它是左起第 9 位).
What's a fast way to find the first bit that is set in this bit array? All the related solutions I have looked up find the first least significant bit, but I need the first most significant one. So, given 0x00A1, I want 8 (since it's the 9th bit from the left).
推荐答案
GCC 有 __builtin_clz 在 x86/x64 上转换为 BSR，在 ARM 上转换为 CLZ 等，并在硬件未实现的情况下模拟指令.
Visual C++ 2005 及更高版本具有 _BitScanReverse.
GCC has __builtin_clz that translates to BSR on x86/x64, CLZ on ARM, etc. and emulates the instruction if the hardware does not implement it.
Visual C++ 2005 and up has _BitScanReverse.
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