Support proper %g, %f, and %a float formatting

See #61
See #104

libc/stdio/dtoa.c

@@ -0,0 +1,25 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/fmt/fmts.h"
+#include "third_party/gdtoa/gdtoa.h"
+
+char *__fmt_dtoa(double d0, int mode, int ndigits, int *decpt, int *sign,
+                 char **rve) {
+  return dtoa(d0, mode, ndigits, decpt, sign, rve);
+}

libc/stdio/printf.c

@@ -58,7 +58,7 @@
  *   This means it implies the quoting modifier, wraps the value with
  *   {,u,L}['"] quotes, displays NULL as "NULL" rather than "(null)".
  *
- * @see palandprintf() for intuitive reference documentation
+ * @see __fmt() for intuitive reference documentation
  * @see {,v}{,s{,n},{,{,x}as},f,d}printf
  */
 int(printf)(const char* fmt, ...) {

libc/stdio/stdio.h

@@ -8,6 +8,9 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 
+int Printf(const char *, ...);
+int Sprintf(char *, const char *, ...);
+
 /*───────────────────────────────────────────────────────────────────────────│─╗
 │ cosmopolitan § standard i/o                                              ─╬─│┼
 ╚────────────────────────────────────────────────────────────────────────────│*/

libc/stdio/stdio.mk

@@ -37,7 +37,8 @@ LIBC_STDIO_A_DIRECTDEPS =				\
 	LIBC_STR					\
 	LIBC_STUBS					\
 	LIBC_SYSV					\
-	LIBC_SYSV_CALLS
+	LIBC_SYSV_CALLS					\
+	THIRD_PARTY_GDTOA
 
 LIBC_STDIO_A_DEPS :=					\
 	$(call uniq,$(foreach x,$(LIBC_STDIO_A_DIRECTDEPS),$($(x))))

libc/stdio/vfprintf.c

@@ -33,7 +33,7 @@ static noinstrument int vfprintfputchar(int c, struct state *st) {
 
 int(vfprintf)(FILE *f, const char *fmt, va_list va) {
   struct state st[1] = {{f, 0}};
-  if (palandprintf(vfprintfputchar, st, fmt, va) != -1) {
+  if (__fmt(vfprintfputchar, st, fmt, va) != -1) {
     return st->n;
   } else {
     return -1;