[U-Boot] [PATCH v2 02/11] lib: charset: add u16_strncmp()

[Heinrich Schuchardt]

On 4/24/19 8:30 AM, AKASHI Takahiro wrote:
> u16_strncmp() works like u16_strcmp() but only at most n characters
> (in u16) are compared.
> This function will be used in a later patch.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
>   include/charset.h |  5 +++++
>   lib/charset.c     | 13 +++++++++++++
>   2 files changed, 18 insertions(+)
>
> diff --git a/include/charset.h b/include/charset.h
> index 747a9b376c03..49842a88bc8b 100644
> --- a/include/charset.h
> +++ b/include/charset.h
> @@ -171,6 +171,11 @@ s32 utf_to_upper(const s32 code);
>    */
>   int u16_strcmp(const u16 *s1, const u16 *s2);
>
> +/*
> + * u16_strncmp() - strncmp() for u16 strings

  * u16_strncmp() - compare two u16 string
  *
  * @s1:		first string to compare
  * @s2:		second string to compare
  * @n1:		maximum number of u16 to compare
  * Return:	0  if the first n u16 are the same in s1 and s2
  *		< 0 if the first different u16 in s1 is less than the
  *		corresponding u16 in s2
  *		> 0 if the first different u16 in s1 is greater than the
  *		corresponding u16 in s2

> + */
> +int u16_strncmp(const u16 *s1, const u16 *s2, size_t n);
> +
>   /**
>    * u16_strlen - count non-zero words
>    *
> diff --git a/lib/charset.c b/lib/charset.c
> index 4a25ac0bdb9c..85f08db68fe2 100644
> --- a/lib/charset.c
> +++ b/lib/charset.c
> @@ -345,6 +345,19 @@ int u16_strcmp(const u16 *s1, const u16 *s2)
>   	return (*(uint16_t *)s1 - *(uint16_t *)s2);
>   }
>
> +int u16_strncmp(const u16 *s1, const u16 *s2, size_t n)
> +{
> +	while ((n-- > 0) && (*s1 == *s2++)) {
> +		if (*s1++ == 0)
> +			return 0;
> +		if (!n)
> +			return 0;
> +	}
> +	--s2;

For u16_strncmp() called with n = 0 I would prefer to see 0 as return
value instead of the result of an illegal memory access.

> +
> +	return (*(uint16_t *)s1 - *(uint16_t *)s2);

No need for a conversion here.

Let's avoid the superfluous increment/decrement, provide 0 for n = 0,
and make sure that the compiler calculates the difference only once per
loop:

int u16_strncmp(const u16 *s1, const u16 *s2, size_t n)
{
         int ret = 0;

         for (; n; --n, ++s1, ++s2) {
                 ret = *s1 - *s2;
                 if (ret || !*s1)
                         break;
         }
         return ret;
}

I would like to see a unit test in test/unicode_ut.c.
The test should include the n = 0 case.

Best regards

Heinrich

> +}
> +
>   size_t u16_strlen(const u16 *in)
>   {
>   	size_t i;
>