add deprecated (removed from posix) [efg]cvt() functions

these have not been heavily tested, but they should work as described
in the old standards. probably broken for non-finite values...

include/stdlib.h

@@ -134,6 +134,9 @@ void *valloc (size_t);
 void *memalign(size_t, size_t);
 int clearenv(void);
 int ptsname_r(int, char *, size_t);
+char *ecvt(double, int, int *, int *);
+char *fcvt(double, int, int *, int *);
+char *gcvt(double, int, char *);
 #endif
 
 

src/stdlib/ecvt.c

@@ -0,0 +1,19 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+char *ecvt(double x, int n, int *dp, int *sign)
+{
+	static char buf[16];
+	char tmp[32];
+	int i, j;
+
+	if (n-1U > 15) n = 15;
+	sprintf(tmp, "%.*e", n-1, x);
+	i = *sign = (tmp[0]=='-');
+	for (j=0; tmp[i]!='e'; j+=(tmp[i++]!='.'))
+		buf[j] = tmp[i];
+	buf[j] = 0;
+	*dp = atoi(tmp+i+1);
+
+	return buf;
+}

src/stdlib/fcvt.c

@@ -0,0 +1,25 @@
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+char *fcvt(double x, int n, int *dp, int *sign)
+{
+	char tmp[1500];
+	int i, lz;
+
+	if (n > 1400U) n = 1400;
+	sprintf(tmp, "%.*f", n, x);
+	i = (tmp[0] == '-');
+	if (tmp[i] == '0') lz = strspn(tmp+i+2, "0");
+	else lz = -(int)strcspn(tmp+i, ".");
+
+	if (n<=lz) {
+		*sign = i;
+		*dp = 0;
+		if (n>14U) n = 14;
+		return "000000000000000"+14-n;
+	}
+
+	return ecvt(x, n-lz, dp, sign);
+}

src/stdlib/gcvt.c

@@ -0,0 +1,8 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+char *gcvt(double x, int n, char *b)
+{
+	sprintf(b, "%.*g", n, x);
+	return b;
+}