`s_strncpy_n()`, `s_strncat_n()` trivial implementation.

Fortune for naka's current commit: Great blessing − 大吉

src/display.c

@@ -11,6 +11,13 @@
 #define FLAGSET(f, flag) (( (f) & (flag) ) == (flag))
 #define DFLAGSET(f, flagname) FLAGSET(f, DISPF_SHOW_ ## flagname)
 
+#define CMP(x,cmp,y)  ( (x) cmp (y) ? (x) : (y) )
+#define CMPx(x,cmp,y) ({ let _x = (x); let _y = (y); CMP(_x, cmp, _y); })
+#define MIN(x, y) CMP((x), <, (y))
+#define MINx(x, y) CMPx((x), <, (y))
+#define MAX(x, y) CMP((x), >, (y))
+#define MAXx(x, y) CMPx((x), >, (y))
+
 // Returns number of bytes written to `dest`. Otherwise same as `strncpy()`.
 static usize strncpy_n(char*pOUT dest, const char* restrict src, usize n)
 {
@@ -24,13 +31,19 @@ static usize strncpy_n(char*pOUT dest, const char* restrict src, usize n)
 // Will not write past `dn` bytes of `dest`, will not read past `sn` bytes of `src`. Otherwise, same as `strncpy_n()`.
 static usize s_strncpy_n(usize sn, usize dn; char dest[static pOUT dn], usize dn, const char src[static restrict sn], usize sn)
 {
-	TODO("double-bounded strncpy");
+	usize i;
+	usize n = MIN(sn,dn); 
+	for(i=0;i<n;i++)
+		if(! (*dest++ = *src++)) return i;
+	if(i<dn) dest[i] = 0;
+	return i;
 }
 
 // Will not write past `dn` bytes of `dest`, will not read past `sn` bytes of `src`. Otherwise, same as `strncat_n()`.
-static usize s_strncat_n(usize sn, usize dn; char dest[static pOUT dn], usize dn, const char src[static restrict sn], usize sn)
+static inline usize s_strncat_n(usize sn, usize dn; char dest[static pOUT dn], usize dn, const char src[static restrict sn], usize sn)
 {
-	TODO("double-bounded strncat");
+	usize dl = MINx(strlen(dest), dn);
+	return s_strncpy_n(dest + dl, dn - dl, src, sn);
 }
 
 // Returns number of bytes written to (dest+strlen(dest)). Otherwise same as `strncat()`.