Re: [musl] [C23 printf 2/3] C23: implement the wN length specifiers for printf

[Rich Felker <dalias@libc.org>]

[-- Attachment #1: Type: text/plain, Size: 856 bytes --]

On Mon, May 29, 2023 at 09:14:13AM +0200, Jₑₙₛ Gustedt wrote:
> Rich,
> 
> on Fri, 26 May 2023 17:03:58 -0400 you (Rich Felker <dalias@libc.org>)
> wrote:
> 
> > I think you need an extra state that's "plain but not bare" that
> > duplicates only the integer transitions out of it, like the l, ll,
> > etc. prefix states do.
> 
> Hm, the problem is that for the other prefixes the table entries then
> encode the concrete type that is to be expected. We could not do this
> here because the type depends on the requested width. So we would then
> need to "repair" that type after the loop. A `switch` to do that would
> look substantially similar to what is there, now. Do you think that
> would be better?

OK I think I can communicate better with code than natural language
text, so here's a diff, completely untested, of what I had in mind.

Rich

[-- Attachment #2: printf-wprefix.diff --]
[-- Type: text/plain, Size: 1690 bytes --]

diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index a712d80f..a751fbdf 100644
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -33,7 +33,7 @@
 
 enum {
 	BARE, LPRE, LLPRE, HPRE, HHPRE, BIGLPRE,
-	ZTPRE, JPRE,
+	ZTPRE, JPRE, PLAIN, WPRE, W1PRE, W3PRE, W6PRE,
 	STOP,
 	PTR, INT, UINT, ULLONG,
 	LONG, ULONG,
@@ -44,9 +44,10 @@ enum {
 	MAXSTATE
 };
 
-#define S(x) [(x)-'A']
+#define ST_BASE '1'
+#define S(x) [(x)-ST_BASE]
 
-static const unsigned char states[]['z'-'A'+1] = {
+static const unsigned char states[]['z'-ST_BASE+1] = {
 	{ /* 0: bare types */
 		S('d') = INT, S('i') = INT,
 		S('o') = UINT, S('u') = UINT, S('x') = UINT, S('X') = UINT,
@@ -94,10 +95,24 @@ static const unsigned char states[]['z'-'A'+1] = {
 		S('o') = UMAX, S('u') = UMAX,
 		S('x') = UMAX, S('X') = UMAX,
 		S('n') = PTR,
+	}, { /* 8: explicit-width-prefixed bare equivalent */
+		S('d') = INT, S('i') = INT,
+		S('o') = UINT, S('u') = UINT,
+		S('x') = UINT, S('X') = UINT,
+		S('n') = PTR,
+	}, { /* 9: w-prefixed */
+		S('1') = W1PRE, S('3') = W3PRE,
+		S('6') = W6PRE, S('8') = HHPRE,
+	}, { /* 10: w1-prefixed */
+		S('6') = HPRE,
+	}, { /* 11: w3-prefixed */
+		S('2') = PLAIN,
+	}, { /* 12: w6-prefixed */
+		S('4') = LLONG_MAX > LONG_MAX ? LLPRE : LPRE,
 	}
 };
 
-#define OOB(x) ((unsigned)(x)-'A' > 'z'-'A')
+#define OOB(x) ((unsigned)(x)-ST_BASE > 'z'-ST_BASE)
 
 union arg
 {
@@ -547,6 +562,7 @@ static int printf_core(FILE *f, const char *fmt, va_list *ap, union arg *nl_arg,
 		switch(t) {
 		case 'n':
 			switch(ps) {
+			case PLAIN:
 			case BARE: *(int *)arg.p = cnt; break;
 			case LPRE: *(long *)arg.p = cnt; break;
 			case LLPRE: *(long long *)arg.p = cnt; break;