iconv: Add UTF-7-IMAP variant in utf-7.c

UTF-7-IMAP differs from UTF-7 in the followings ways (see RFC 3501[1]
for reference) :

- The shift character is '&' instead of '+'
- There is no "optional direct characters" and the "direct characters"
  set is different
- There is no implicit shift back to US-ASCII from BASE64, all BASE64
  sequences MUST be terminated with '-'

[1]: https://datatracker.ietf.org/doc/html/rfc3501#section-5.1.3

Signed-off-by: Max Gautier <mg@max.gautier.name>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

iconvdata/TESTS

@@ -94,6 +94,7 @@ EUC-TW			EUC-TW			Y	UTF8
 GBK			GBK			Y	UTF8
 BIG5HKSCS		BIG5HKSCS		Y	UTF8
 UTF-7			UTF-7			N	UTF8
+UTF-7-IMAP		UTF-7-IMAP		N	UTF8
 IBM856			IBM856			N	UTF8
 IBM922			IBM922			Y	UTF8
 IBM930			IBM930			N	UTF8

iconvdata/gconv-modules

@@ -113,3 +113,7 @@ module	INTERNAL		UTF-32BE//		UTF-32		1
 alias	UTF7//			UTF-7//
 module	UTF-7//			INTERNAL		UTF-7		1
 module	INTERNAL		UTF-7//			UTF-7		1
+
+#	from			to			module		cost
+module	UTF-7-IMAP//		INTERNAL		UTF-7		1
+module	INTERNAL		UTF-7-IMAP//		UTF-7		1

iconvdata/testdata/UTF-7-IMAP

@@ -0,0 +1 @@
+&EqASGxItEps-       Amharic&AAoBDQ-esky      Czech&AAo-Dansk      Danish&AAo-English    English&AAo-Suomi      Finnish&AAo-Fran&AOc-ais   French&AAo-Deutsch    German&AAoDlQO7A7sDtwO9A7kDugOs-   Greek&AAoF4gXRBegF2QXq-      Hebrew&AAo-Italiano   Italian&AAo-Norsk      Norwegian&AAoEIARDBEEEQQQ6BDgEOQ-    Russian&AAo-Espa&APE-ol    Spanish&AAo-Svenska    Swedish&AAoOIA4yDikOMg5EDhcOIg-    Thai&AAo-T&APw-rk&AOc-e     Turkish&AAo-Ti&Hr8-ng Vi&Hsc-t Vietnamese&AApl5Wcsip4-     Japanese&AApOLWWH-       Chinese&AArVXK4A-       Korean&AAoACg-// Checking for correct handling of shift characters ('&-', '-') after base64 sequences&AArVXK4A-&-&AArVXK4A--&AAoACg-// Checking for correct handling of litteral '&-' and '-'&AAo----&-&--&AAoACg-// The last line of this file is missing the end-of-line terminator&AAo-// on purpose, in order to test that the conversion empties the bit buffer&AAo-// and shifts back to the initial state at the end of the conversion.&AAo-A&ImIDkQ-

iconvdata/testdata/UTF-7-IMAP..UTF8

@@ -0,0 +1,32 @@
+አማርኛ       Amharic
+česky      Czech
+Dansk      Danish
+English    English
+Suomi      Finnish
+Français   French
+Deutsch    German
+Ελληνικά   Greek
+עברית      Hebrew
+Italiano   Italian
+Norsk      Norwegian
+Русский    Russian
+Español    Spanish
+Svenska    Swedish
+ภาษาไทย    Thai
+Türkçe     Turkish
+Tiếng Việt Vietnamese
+日本語     Japanese
+中文       Chinese
+한글       Korean
+
+// Checking for correct handling of shift characters ('&', '-') after base64 sequences
+한글&
+한글-
+
+// Checking for correct handling of litteral '&' and '-'
+---&&-
+
+// The last line of this file is missing the end-of-line terminator
+// on purpose, in order to test that the conversion empties the bit buffer
+// and shifts back to the initial state at the end of the conversion.
+A≢Α

iconvdata/utf-7.c

@@ -33,11 +33,13 @@
 enum variant
 {
   UTF7,
+  UTF_7_IMAP
 };
 
 /* Must be in the same order as enum variant above.  */
 static const char names[] =
   "UTF-7//\0"
+  "UTF-7-IMAP//\0"
   "\0";
 
 static uint32_t
@@ -45,6 +47,8 @@ shift_character (enum variant const var)
 {
   if (var == UTF7)
     return '+';
+  else if (var == UTF_7_IMAP)
+    return '&';
   else
     abort ();
 }
@@ -58,6 +62,9 @@ between (uint32_t const ch,
 
 /* The set of "direct characters":
    A-Z a-z 0-9 ' ( ) , - . / : ? space tab lf cr
+   FOR UTF-7-IMAP
+   A-Z a-z 0-9 ' ( ) , - . / : ? space
+   ! " # $ % + * ; < = > @ [ \ ] ^ _ ` { | } ~
 */
 
 static bool
@@ -71,6 +78,8 @@ isdirect (uint32_t ch, enum variant var)
 	    || between (ch, ',', '/')
 	    || ch == ':' || ch == '?'
 	    || ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r');
+  else if (var == UTF_7_IMAP)
+    return (ch != '&' && between (ch, ' ', '~'));
   abort ();
 }
 
@@ -124,6 +133,8 @@ base64 (unsigned int i, enum variant var)
     return '+';
   else if (i == 63 && var == UTF7)
     return '/';
+  else if (i == 63 && var == UTF_7_IMAP)
+    return ',';
   else
     abort ();
 }
@@ -308,7 +319,8 @@ gconv_end (struct __gconv_step *data)
 	  i = ch - '0' + 52;						      \
 	else if (ch == '+')						      \
 	  i = 62;							      \
-	else if (ch == '/')						      \
+	else if ((var == UTF7 && ch == '/')                                   \
+		  || (var == UTF_7_IMAP && ch == ','))			      \
 	  i = 63;							      \
 	else								      \
 	  {								      \
@@ -316,8 +328,10 @@ gconv_end (struct __gconv_step *data)
 									      \
 	    /* If accumulated data is nonzero, the input is invalid.  */      \
 	    /* Also, partial UTF-16 characters are invalid.  */		      \
-	    if (__builtin_expect (statep->__value.__wch != 0, 0)	      \
+	    /* In IMAP variant, must be terminated by '-'.  */		      \
-		|| __builtin_expect ((statep->__count >> 3) <= 26, 0))	      \
+	    if (__glibc_unlikely (statep->__value.__wch != 0)		      \
+		|| __glibc_unlikely ((statep->__count >> 3) <= 26)	      \
+		|| __glibc_unlikely (var == UTF_7_IMAP && ch != '-'))	      \
 	      {								      \
 		STANDARD_FROM_LOOP_ERR_HANDLER ((statep->__count = 0, 1));    \
 	      }								      \
@@ -474,13 +488,15 @@ gconv_end (struct __gconv_step *data)
     else								      \
       {									      \
 	/* base64 encoding active */					      \
-	if (isdirect (ch, var))						      \
+	if ((var == UTF_7_IMAP && ch == '&') || isdirect (ch, var))	      \
 	  {								      \
 	    /* deactivate base64 encoding */				      \
 	    size_t count;						      \
 									      \
 	    count = ((statep->__count & 0x18) >= 0x10)			      \
-	      + needs_explicit_shift (ch) + 1;				      \
+	      + (var == UTF_7_IMAP || needs_explicit_shift (ch))	      \
+	      + (var == UTF_7_IMAP && ch == '&')			      \
+	      + 1;							      \
 	    if (__glibc_unlikely (outptr + count > outend))		      \
 	      {								      \
 		result = __GCONV_FULL_OUTPUT;				      \
@@ -489,9 +505,11 @@ gconv_end (struct __gconv_step *data)
 									      \
 	    if ((statep->__count & 0x18) >= 0x10)			      \
 	      *outptr++ = base64 ((statep->__count >> 3) & ~3, var);	      \
-	    if (needs_explicit_shift (ch))				      \
+	    if (var == UTF_7_IMAP || needs_explicit_shift (ch))		      \
 	      *outptr++ = '-';						      \
 	    *outptr++ = (unsigned char) ch;				      \
+	    if (var == UTF_7_IMAP && ch == '&')				      \
+	      *outptr++ = '-';						      \
 	    statep->__count = 0;					      \
 	  }								      \
 	else								      \