• State Suggested Answer
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 21 subscribers
  • Views 2543 views
  • Users 0 members are here
Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

question about __builtin_ctz

zxczxca

Hi, I have a question. I used '__builtin_ctz' function in arm compiler and it worked well, but I don't know  which header file contains '__builtin_ctz' function. Do you know which header file is needed to use '__builtin_ctz' function?

Parents
  • 0

    You can apparently find it (eventually) in the gcc source code.  It wasn't as easy as it should have been.
    Check out ...gcc-arm-src-10.3-2021.10/src/gcc/libgcc/config/arm/lib1funcs.S

    the 32bit function is actually called "ctzsi2":

    ARM_FUNC_START ctzsi2
        rsb    r1, r0, #0
        and    r0, r0, r1
    # if defined (__ARM_FEATURE_CLZ)
        clz    r0, r0
        rsb    r0, r0, #31
        RET

    The source code is rather obscured by conditionals for the various ARM architectures, and doesn't seem to have any comments.  You may be better off compiling for your desired target system and looking at the disassembly.

Reply
  • 0

    You can apparently find it (eventually) in the gcc source code.  It wasn't as easy as it should have been.
    Check out ...gcc-arm-src-10.3-2021.10/src/gcc/libgcc/config/arm/lib1funcs.S

    the 32bit function is actually called "ctzsi2":

    ARM_FUNC_START ctzsi2
        rsb    r1, r0, #0
        and    r0, r0, r1
    # if defined (__ARM_FEATURE_CLZ)
        clz    r0, r0
        rsb    r0, r0, #31
        RET

    The source code is rather obscured by conditionals for the various ARM architectures, and doesn't seem to have any comments.  You may be better off compiling for your desired target system and looking at the disassembly.

Children
No data