libutils: add kernel word size related CTZ macro

[colorglass]

Add kernel word size related macros CxZ_WORD() for ctz and clz builtin func. And also add CxZLL() macro for 64bits data size.
And for the macro CTZL(), which is used for unsigned long type, I found a error use in sel4test timer dirver: https://github.com/seL4/sel4test/blob/0a488b92bc7a08acc14d49524d1f22656f286627/apps/sel4test-driver/src/timer.c#L53

......
void handle_timer_interrupts(driver_env_t env, seL4_Word badge)
{
    int error = 0;
    while (badge) {
        seL4_Word badge_bit = CTZL(badge);
......

The seL4_Word type can be 64bits, but CTZL() recives unsigned long argument. It can be changed to CTZ_WORD() to fix the problom.

[axel-h]

Let's group the variants together and issue a warning if CONFIG_WORD_SIZE is invalid. Also do some sanity checking that the types match. Userland libraries could be compiles with any settings.

    #include "compile_time.h"

    ....

    #if CONFIG_WORD_SIZE == 32

    #define BSWAP_WORD(x) __builtin_bswap32(x)
    compile_time_assert(long_is_32_bit, sizeof(long) == 4)
    #define CTZ_WORD(x) CTZL(x)
    #define CLZ_WORD(x) CLZL(x)

    #elif CONFIG_WORD_SIZE == 64

    #define BSWAP_WORD(x) __builtin_bswap64(x)
    compile_time_assert(long_is_64_bit, sizeof(long long) == 8)
    #define CTZ_WORD(x) CTZLL(x)
    #define CLZ_WORD(x) CLZLL(x)

    #else
    /*
     *  This library aims to be agnostic of the "word" concept, so don't raise an
     *  error if CONFIG_WORD_SIZE is unsupported or not set. We just don't provide
     *  the macros at all in this case.
     */
    #endif

[axel-h]

Actually, on 64-bit systems, it is quite common that long is 64-bit. So we could also go with #define CTZ_WORD(x) CTZL() in both cases. Note that In libutils/include/utils/arith.h this lib already uses CTZL().

[colorglass]

You are right, but I tested it using both x64 and arm64 msvc 19.30 and get that long is 32bits size. So I suggest that we use the more likely selection for word size type.

[axel-h]

Oh - if long is 32-bit on a 64-bit architecture, I'd expect this to break a lot more things...

[lsf37]

long is definitely 64 on the compilers that are supported for the 64 bit architectures that are supported.

[colorglass]

Thanks for your attention.

I searched C99 standard ISO/IEC 9899:1999, and didn't find the size define of long, only got some information indicates that it should hold the number limits defined in limits.h.

And I find that the size of long in gcc was defined by a internal macro LONG_TYPE_SIZE Layout of Source Language Data Types, which defines that long type in gcc has the default one word size.

Finally I write the simple test file to print the result of sizeof(long), compile and run and get the result is 4 within my visual studio 2019.

So I can confirm that the practical size of the long is depended on the compiler itself. The most generally used compiler is gcc and one word size long becomes a de facto standard.

Please forgive my attention to details, and since there is no builtin_ctz() function in msvc, we can just apply CTZL() to word size variable with no change to this file.

[axel-h]

See explanation here: https://en.m.wikipedia.org/wiki/64-bit_computing
Seems LLP64 support for userland is currently not planned then.