[PATCH v5 2/4] iconv: Better mapping to RFC for UTF-7

[Adhemerval Zanella]

On 20/03/2022 13:41, Max Gautier via Libc-alpha wrote:
> - Direct use of characters instead of arcane arrays
> - isxbase64 is not the Modified BASE64 alphabet, but the characters who
>   needs to trigger an explicit shift back to US-ASCII. Make that clearer
> 
> Signed-off-by: Max Gautier <mg@max.gautier.name>


LGTM, thanks.

Reviewed-by: Adhemerval Zanellla  <adhemerval.zanella@linaro.org>

> ---
>  iconvdata/utf-7.c | 64 ++++++++++++++++++++++++-----------------------
>  1 file changed, 33 insertions(+), 31 deletions(-)
> 
> diff --git a/iconvdata/utf-7.c b/iconvdata/utf-7.c
> index 9ba0974959..15f3669ac8 100644
> --- a/iconvdata/utf-7.c
> +++ b/iconvdata/utf-7.c
> @@ -30,20 +30,27 @@
>  
>  
>  
> +static bool
> +between (uint32_t const ch,
> +	 uint32_t const lower_bound, uint32_t const upper_bound)
> +{
> +  return (ch >= lower_bound && ch <= upper_bound);
> +}
> +
>  /* The set of "direct characters":
>     A-Z a-z 0-9 ' ( ) , - . / : ? space tab lf cr
>  */
>  
> -static const unsigned char direct_tab[128 / 8] =
> -  {
> -    0x00, 0x26, 0x00, 0x00, 0x81, 0xf3, 0xff, 0x87,
> -    0xfe, 0xff, 0xff, 0x07, 0xfe, 0xff, 0xff, 0x07
> -  };
> -
> -static int
> -isdirect (uint32_t ch)
> +static bool
> +isdirect (uint32_t ch, enum variant var)
>  {
> -  return (ch < 128 && ((direct_tab[ch >> 3] >> (ch & 7)) & 1));
> +  return (between (ch, 'A', 'Z')
> +	  || between (ch, 'a', 'z')
> +	  || between (ch, '0', '9')
> +	  || ch == '\'' || ch == '(' || ch == ')'
> +	  || between (ch, ',', '/')
> +	  || ch == ':' || ch == '?'
> +	  || ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r');
>  }
>  
>  
> @@ -52,33 +59,27 @@ isdirect (uint32_t ch)
>     ! " # $ % & * ; < = > @ [ ] ^ _ ` { | }
>  */
>  
> -static const unsigned char xdirect_tab[128 / 8] =
> -  {
> -    0x00, 0x26, 0x00, 0x00, 0xff, 0xf7, 0xff, 0xff,
> -    0xff, 0xff, 0xff, 0xef, 0xff, 0xff, 0xff, 0x3f
> -  };
> -
> -static int
> -isxdirect (uint32_t ch)
> +static bool
> +isxdirect (uint32_t ch, enum variant var)
>  {
> -  return (ch < 128 && ((xdirect_tab[ch >> 3] >> (ch & 7)) & 1));
> +  return (ch == '\t'
> +	  || ch == '\n'
> +	  || ch == '\r'
> +	  || (between (ch, ' ', '}') && ch != '+' && ch != '\\'));
>  }
>  
>  
> -/* The set of "extended base64 characters":
> +/* Characters which needs to trigger an explicit shift back to US-ASCII (UTF-7
> +   only): Modified base64 + '-' (shift back character)
>     A-Z a-z 0-9 + / -
>  */
>  
> -static const unsigned char xbase64_tab[128 / 8] =
> -  {
> -    0x00, 0x00, 0x00, 0x00, 0x00, 0xa8, 0xff, 0x03,
> -    0xfe, 0xff, 0xff, 0x07, 0xfe, 0xff, 0xff, 0x07
> -  };
> -
> -static int
> -isxbase64 (uint32_t ch)
> +static bool
> +needs_explicit_shift (uint32_t ch)
>  {
> -  return (ch < 128 && ((xbase64_tab[ch >> 3] >> (ch & 7)) & 1));
> +  return (between (ch, 'A', 'Z')
> +	  || between (ch, 'a', 'z')
> +	  || between (ch, '/', '9') || ch == '+' || ch == '-');
>  }
>  
>  
> @@ -252,7 +253,7 @@ base64 (unsigned int i)
>  		   indeed form a Low Surrogate.  */			      \
>  		uint32_t wc2 = wch & 0xffff;				      \
>  									      \
> -		if (! __builtin_expect (wc2 >= 0xdc00 && wc2 < 0xe000, 1))    \
> +		if (! __glibc_likely (wc2 >= 0xdc00 && wc2 < 0xe000))	      \
>  		  {							      \
>  		    STANDARD_FROM_LOOP_ERR_HANDLER ((statep->__count = 0, 1));\
>  		  }							      \
> @@ -372,7 +373,8 @@ base64 (unsigned int i)
>  	    /* deactivate base64 encoding */				      \
>  	    size_t count;						      \
>  									      \
> -	    count = ((statep->__count & 0x18) >= 0x10) + isxbase64 (ch) + 1;  \
> +	    count = ((statep->__count & 0x18) >= 0x10)			      \
> +	      + needs_explicit_shift (ch) + 1;				      \
>  	    if (__glibc_unlikely (outptr + count > outend))		      \
>  	      {								      \
>  		result = __GCONV_FULL_OUTPUT;				      \
> @@ -381,7 +383,7 @@ base64 (unsigned int i)
>  									      \
>  	    if ((statep->__count & 0x18) >= 0x10)			      \
>  	      *outptr++ = base64 ((statep->__count >> 3) & ~3);		      \
> -	    if (isxbase64 (ch))						      \
> +	    if (needs_explicit_shift (ch))				      \
>  	      *outptr++ = '-';						      \
>  	    *outptr++ = (unsigned char) ch;				      \
>  	    statep->__count = 0;					      \