Re: [kvm-unit-tests PATCH v2 10/23] lib/printf: Add support for printing wide strings

[Ricardo Koller <ricarkol@google.com>]

On Fri, May 06, 2022 at 09:55:52PM +0100, Nikos Nikoleris wrote:
> This change adds support for wide strings (u16*) to printf()
> variants. This feature is used by a future change.
> 
> Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
> ---
>  lib/printf.c | 101 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 100 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/printf.c b/lib/printf.c
> index 724befa..14a3fed 100644
> --- a/lib/printf.c
> +++ b/lib/printf.c
> @@ -57,6 +57,102 @@ static void print_str(pstream_t *p, const char *s, strprops_t props)
>      }
>  }
>  
> +/*
> + * Adapted from drivers/firmware/efi/libstub/vsprintf.c
> + */
> +static u32 utf16_to_utf32(const u16 **s16)
> +{
> +    u16 c0, c1;
> +
> +    c0 = *(*s16)++;
> +    /* not a surrogate */
> +    if ((c0 & 0xf800) != 0xd800)
> +	return c0;
> +    /* invalid: low surrogate instead of high */
> +    if (c0 & 0x0400)
> +	return 0xfffd;
> +    c1 = **s16;
> +    /* invalid: missing low surrogate */
> +    if ((c1 & 0xfc00) != 0xdc00)
> +	return 0xfffd;
> +    /* valid surrogate pair */
> +    ++(*s16);
> +    return (0x10000 - (0xd800 << 10) - 0xdc00) + (c0 << 10) + c1;
> +}
> +
> +/*
> + * Adapted from drivers/firmware/efi/libstub/vsprintf.c
> + */
> +static size_t utf16s_utf8nlen(const u16 *s16, size_t maxlen)
> +{
> +    size_t len, clen;
> +
> +    for (len = 0; len < maxlen && *s16; len += clen) {
> +	u16 c0 = *s16++;
> +
> +	/* First, get the length for a BMP character */
> +	clen = 1 + (c0 >= 0x80) + (c0 >= 0x800);
> +	if (len + clen > maxlen)
> +	    break;
> +	/*
> +	 * If this is a high surrogate, and we're already at maxlen, we
> +	 * can't include the character if it's a valid surrogate pair.
> +	 * Avoid accessing one extra word just to check if it's valid
> +	 * or not.
> +	 */
> +	if ((c0 & 0xfc00) == 0xd800) {
> +	    if (len + clen == maxlen)
> +		break;
> +	    if ((*s16 & 0xfc00) == 0xdc00) {
> +		++s16;
> +		++clen;
> +	    }
> +	}
> +    }
> +
> +    return len;
> +}
> +
> +/*
> + * Adapted from drivers/firmware/efi/libstub/vsprintf.c
> + */
> +static void print_wstring(pstream_t *p, const u16 *s, strprops_t props)
> +{
> +    const u16 *ws = (const u16 *)s;
> +    size_t pos = 0, size = p->remain + 1, len = utf16s_utf8nlen(ws, props.precision);
> +
> +    while (len-- > 0) {
> +	u32 c32 = utf16_to_utf32(&ws);
> +	u8 *s8;
> +	size_t clen;
> +
> +	if (c32 < 0x80) {
> +	    addchar(p, c32);
> +	    continue;
> +	}
> +
> +	/* Number of trailing octets */
> +	clen = 1 + (c32 >= 0x800) + (c32 >= 0x10000);
> +
> +	len -= clen;
> +	s8 = (u8 *)(p->buffer - p->added + pos);
> +
> +	/* Avoid writing partial character */
> +	addchar(p, '\0');
> +	pos += clen;
> +	if (pos >= size)
> +	    continue;
> +
> +	/* Set high bits of leading octet */
> +	*s8 = (0xf00 >> 1) >> clen;
> +	/* Write trailing octets in reverse order */
> +	for (s8 += clen; clen; --clen, c32 >>= 6)
> +	    *s8-- = 0x80 | (c32 & 0x3f);
> +	/* Set low bits of leading octet */
> +	*s8 |= c32;
> +    }
> +}
> +
>  static char digits[16] = "0123456789abcdef";
>  
>  static void print_int(pstream_t *ps, long long n, int base, strprops_t props)
> @@ -302,7 +398,10 @@ int vsnprintf(char *buf, int size, const char *fmt, va_list va)
>  	    print_unsigned(&s, (unsigned long)va_arg(args, void *), 16, props);
>  	    break;
>  	case 's':
> -	    print_str(&s, va_arg(args, const char *), props);
> +	    if (nlong)
> +		print_wstring(&s, va_arg(args, const u16 *), props);
> +	    else
> +		print_str(&s, va_arg(args, const char *), props);
>  	    break;
>  	default:
>  	    addchar(&s, f);
> -- 
> 2.25.1
>

Reviewed-by: Ricardo Koller <ricarkol@google.com>