Centered fields in format.

* stream.c (enum align): New enum.
(vformat_align_pre, vformat_align_post): New static functions.
(vformat_num, vformat_str): Argument left renamed to align, and changed
to enum align. vformat_align_pre and vformat_align_post are called to
generate the correct padding for left, center and right alignment.
(vformat): Two-valued local variable left turned into three-valued
align. The ^ prefix on the width field is recognized.

* txr.1: Documented ^ width prefix.

3 files changed, 96 insertions, 31 deletions

diff --git a/ChangeLog b/ChangeLog
index 75601567..bea91235 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,19 @@
 2015-07-28  Kaz Kylheku  <kaz@kylheku.com>
 
+	Centered fields in format.
+
+	* stream.c (enum align): New enum.
+	(vformat_align_pre, vformat_align_post): New static functions.
+	(vformat_num, vformat_str): Argument left renamed to align, and changed
+	to enum align. vformat_align_pre and vformat_align_post are called to
+	generate the correct padding for left, center and right alignment.
+	(vformat): Two-valued local variable left turned into three-valued
+	align. The ^ prefix on the width field is recognized.
+
+	* txr.1: Documented ^ width prefix.
+
+2015-07-28  Kaz Kylheku  <kaz@kylheku.com>
+
 	* share/txr/stdlib/txr-case.tl (txr-case-impl): Bugfix,
 	handle nil case in recursion.
 
diff --git a/stream.c b/stream.c
index 30c77ee3..e84025d5 100644
--- a/stream.c
+++ b/stream.c
@@ -1825,8 +1825,54 @@ static void detect_format_string(void)
   }
 }
 
+enum align { al_left, al_center, al_right };
+
+static val vformat_align_pre(val stream, enum align align, int slack)
+{
+  int i;
+
+  switch (align) {
+  case al_right:
+    for (i = 0; i < slack; i++)
+      if (!put_char(chr(' '), stream))
+        return nil;
+    break;
+  case al_left:
+    break;
+  case al_center:
+    for (i = 0; i < slack/2; i++)
+      if (!put_char(chr(' '), stream))
+        return nil;
+    break;
+  }
+
+  return t;
+}
+
+static val vformat_align_post(val stream, enum align align, int slack)
+{
+  int i;
+
+  switch (align) {
+  case al_right:
+    break;
+  case al_left:
+    for (i = 0; i < slack; i++)
+      if (!put_char(chr(' '), stream))
+        return nil;
+    break;
+  case al_center:
+    for (i = 0; i < (slack+1)/2; i++)
+      if (!put_char(chr(' '), stream))
+        return nil;
+    break;
+  }
+
+  return t;
+}
+
 static val vformat_num(val stream, const char *str,
-                       int width, int left, int zeropad,
+                       int width, enum align align, int zeropad,
                        int precision, int sign)
 {
   int sign_char = (str[0] == '-' || str[0] == '+') ? str[0] : 0;
@@ -1836,10 +1882,8 @@ static val vformat_num(val stream, const char *str,
   int slack = (total_len < width) ? width - total_len : 0;
   int i;
 
-  if (!left)
-    for (i = 0; i < slack; i++)
-      if (!put_char(chr(' '), stream))
-        return nil;
+  if (!vformat_align_pre(stream, align, slack))
+    return nil;
 
   if (!zeropad)
     for (i = 0; i < padlen; i++)
@@ -1862,15 +1906,10 @@ static val vformat_num(val stream, const char *str,
     if (!put_char(chr(*str++), stream))
       return nil;
 
-  if (left)
-    for (i = 0; i < slack; i++)
-      if (!put_char(chr(' '), stream))
-        return nil;
-
-  return t;
+  return vformat_align_post(stream, align, slack);
 }
 
-static val vformat_str(val stream, val str, int width, int left,
+static val vformat_str(val stream, val str, int width, enum align align,
                        int precision)
 {
   const wchar_t *cstr = c_str(str);
@@ -1881,7 +1920,10 @@ static val vformat_str(val stream, val str, int width, int left,
 
   prot1(&str);
 
-  if (!left)
+  if (!vformat_align_pre(stream, align, slack))
+    goto nilout;
+
+  if (!al_left)
     for (i = 0; i < slack; i++)
       if (!put_char(chr(' '), stream))
         goto nilout;
@@ -1890,10 +1932,8 @@ static val vformat_str(val stream, val str, int width, int left,
     if (!put_char(chr(cstr[i]), stream))
       goto nilout;
 
-  if (left)
-    for (i = 0; i < slack; i++)
-      if (!put_char(chr(' '), stream))
-        goto nilout;
+  if (!vformat_align_post(stream, align, slack))
+    goto nilout;
 
   rel1(&str);
   return t;
@@ -1917,7 +1957,8 @@ val vformat(val stream, val fmtstr, va_list vl)
       vf_init, vf_width, vf_digits, vf_star, vf_precision, vf_spec
     } state = vf_init, saved_state = vf_init;
     int width = 0, precision = 0, precision_p = 0, digits = 0;
-    int left = 0, sign = 0, zeropad = 0;
+    enum align align = al_right;
+    int sign = 0, zeropad = 0;
     cnum value;
 
     for (;;) {
@@ -1933,7 +1974,7 @@ val vformat(val stream, val fmtstr, va_list vl)
         case '~':
           state = vf_width;
           width = 0;
-          left = 0;
+          align = al_right;
           zeropad = 0;
           precision = 0;
           precision_p = 0;
@@ -1951,7 +1992,10 @@ val vformat(val stream, val fmtstr, va_list vl)
           state = vf_init;
           continue;
         case '<':
-          left = 1;
+          align = al_left;
+          continue;
+        case '^':
+          align = al_center;
           continue;
         case ',':
           state = vf_precision;
@@ -2010,7 +2054,7 @@ val vformat(val stream, val fmtstr, va_list vl)
           case vf_width:
             if (width < 0) {
               width = -digits;
-              left = 1;
+              align = al_left;
             } else {
               width = digits;
             }
@@ -2134,7 +2178,7 @@ val vformat(val stream, val fmtstr, va_list vl)
             }
             if (!isdigit(num_buf[0]) && !isdigit(num_buf[1])) {
               if (!vformat_str(stream, lit("#<bad-float>"),
-                               width, left, 0))
+                               width, align, 0))
                 goto nilout;
               continue;
             }
@@ -2195,7 +2239,7 @@ val vformat(val stream, val fmtstr, va_list vl)
 
             if (!isdigit(num_buf[0]) && !isdigit(num_buf[1])) {
               if (!vformat_str(stream, lit("#<bad-float>"),
-                               width, left, 0))
+                               width, align, 0))
                 goto nilout;
               continue;
             }
@@ -2206,7 +2250,7 @@ val vformat(val stream, val fmtstr, va_list vl)
             if (width != 0 || precision_p) {
               val str = format(nil, ch == 'a' ? lit("~a") : lit("~s"),
                                obj, nao);
-              if (!vformat_str(stream, str, width, left, precision))
+              if (!vformat_str(stream, str, width, align, precision))
                 goto nilout;
               continue;
             }
@@ -2228,7 +2272,7 @@ val vformat(val stream, val fmtstr, va_list vl)
                     chr(ch), nao);
         output_num:
           {
-            val res = vformat_num(stream, pnum, width, left,
+            val res = vformat_num(stream, pnum, width, align,
                                   zeropad, precision, sign);
             if (pnum != num_buf)
               free(pnum);
diff --git a/txr.1 b/txr.1
index a9e46876..1f05ea20 100644
--- a/txr.1
+++ b/txr.1
@@ -23979,13 +23979,18 @@ are specified as follows:
 .meIP < width
 The width specifier consists of an optional
 .code <
-(left angle bracket) character,
-followed by an optional width specification.
+(left angle bracket) character or
+.code ^
+(caret)
+character followed by an optional width specification.
 
 If the leading
 .code <
 character is present, then the printing will be left-adjusted within
-this field. Otherwise it will be right-adjusted by default.
+this field. If the
+.code ^
+character is present, the printing will be centered within the field.
+Otherwise it will be right-adjusted by default.
 
 The width can be specified as a decimal integer, or as the character
 .codn * .
@@ -23994,10 +23999,12 @@ The
 notation means that instead of digits, the value of the next argument is
 consumed, and expected to be an integer which specifies the width. If that
 integer value is negative, then the field will be left-adjusted.
-If the value is positive, but the
+If the value is positive, but either the
 .code <
-character is present in the width
-specifier, then the field is left adjusted.
+or
+.code ^
+prefix character is present in the width
+specifier, then the field is adjusted according to that character.
 
 .meIP < precision
 The precision specifier is introduced by a leading comma. If this comma appears