将按位操作从C＃移植到C

Question

I need some help porting this C# code over to C. I have it working in C# just fine but I'm getting the wrong return in C. Should I be breaking down the bit shifting into separate lines? I thought I had an issue with the data types but I think I have the right ones. Here was the working code that returns 0x03046ABE

  UInt32 goHigh(UInt32 x) { return (UInt32)(x & 0xFFFF0000); }          
  UInt32 goLow(UInt32 x) { return (UInt32)(x & 0xFFFF); } 

  UInt32 magic(UInt32 pass){
      UInt32 key = pass;
      UInt16 num = 0x0563;
      key = (goLow(key) << 16) | (UInt16)(((num >> 3) | (num << 13)) ^ (goHigh(key) >> 16));
      return key; //returns 0x03046ABE

   }

  magic(0x01020304);

This was the incorrect C code that I'm trying to get working

  unsigned long  goHigh(unsigned long  x) { 
         return (unsigned long )(x & 0xFFFF0000); }          
  unsigned long  goLow(unsigned long  x) { 
         return (unsigned long )(x & 0xFFFF); } 

  unsigned long  magic(unsigned long  pass){
      unsigned long key = pass;
      unsigned int num = 0x0563;
      key = (goLow(key) << 16) | (unsigned int)(((num >> 3) | (num << 13)) ^ (goHigh(key) >> 16));
      return key;
  }

  magic(0x01020304); //returns 0xb8c6a8e

Answer 1

Most likely problem is here:

key = (goLow(key) << 16) | (unsigned int)(((num >> 3) | (num << 13)) ^ (goHigh(key) >> 16));
                            ^^^^^^^^^^^^

which you expect is 16-bit. It may be larger on different machines. Same with unsigned long, which may be 64-bit instead of 32, as you expect.

To be sure, use uint32_t & uint16_t . You have to #include <stdint.h> to be able to use them.

Answer 2

long and int are not the sizes you expect on your platform (32 and 16 bits respectively)

Replace the primitive types with the actual sizes and it will be the same output. I've also removed redundant casts.

These types can be found in stdint.h

#include <stdint.h>

    uint32_t  goHigh(uint32_t   x) {
        return (x & 0xFFFF0000);
    }

    uint32_t goLow(uint32_t x) {
        return (x & 0xFFFF);
    }

    uint32_t magic(uint32_t pass) {
        uint32_t  key = pass;
        uint32_t num = 0x0563;
        key = (goLow(key) << 16) | (uint16_t)(((num >> 3) | (num << 13)) ^ (goHigh(key) >> 16));
        return key;
    }