[PATCH v4 2/4] iconv: Better mapping to RFC for UTF-7

[Max Gautier <mg@max.gautier.name>]

- 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>
---
 iconvdata/utf-7.c | 56 +++++++++++++++++++++++++++--------------------
 1 file changed, 32 insertions(+), 24 deletions(-)

diff --git a/iconvdata/utf-7.c b/iconvdata/utf-7.c
index 9ba0974959..ac7d78141a 100644
--- a/iconvdata/utf-7.c
+++ b/iconvdata/utf-7.c
@@ -30,20 +30,27 @@
 
 
 
+static int
+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)
 {
-  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 +59,33 @@ 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)
 {
-  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)
+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 == '-'
+          );
 }
 
 
@@ -372,7 +379,8 @@ 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 +389,7 @@ 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;					      \
-- 
2.34.1