How to Efficiently Calculate Integer Log2 in C Without Floating-Point Errors?

Integer Log2 Computation in C

Expanding on the given question, which seeks a method to perform an integer log2 operation in C without encountering floating-point approximation issues, we delve into a solution. The C standard libraries do not provide an integer implementation of log, complicating the computation of an index's level in a binary tree using log(index) / log(2).

To address this, the inline ASM function provided utilizes the bsr instruction on x86 or x86-64 platforms. This instruction provides the position of the highest set bit in an unsigned integer, which is equivalent to log2(). The implementation utilizes the inline ASM functionality.

#include <stdint.h>
static inline uint32_t log2(const uint32_t x) {
  uint32_t y;
  asm ( "\tbsr %1, %0\n"
      : "=r"(y)
      : "r" (x)
  );
  return y;
}

By leveraging this method, you can accurately determine the index's level in the binary tree, even for edge elements where value = 2^n.

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