further optimizations

k&r/04-funcs-and-prog-struct/04-grep-grace.c

@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <string.h>
-
-#define LNBUFF_LEN 10
+#include <math.h>
+#include <assert.h>
 
 int grep(char pattern[]);
 
@@ -67,54 +67,52 @@ void println()
 
 /* ------------------------ line buffer ---------------------- */
 
+#define LNBUFF_LEN 8
+
+/* the line buffer lenght must be a power of two */
+static_assert(!(LNBUFF_LEN % 2), "Line buffer length is not a power of two!");
 
 /* line_buffer: global overflowing line buffer */
 struct {
     char self[LNBUFF_LEN];
-    unsigned i;
-    unsigned trunc;
-} lnbuff = {.i = 0, .trunc = 0};
+    unsigned len;
+} lnbuff = {.len= 0};
 
-/* reset_lnbuff: reset buffer */
-#define reset_lnbuff() lnbuff.i = lnbuff.trunc = 0
+/* LNBUFF_I: current index in line buffer */
+#define LNBUFF_I (lnbuff.len & (LNBUFF_LEN - 1))
 
 /* getch_lnbuff: getchar and add it to buffer */
 int getch_lnbuff()
 {
     int c = getchar();
     
-    if (c == EOF || c == '\n') { // new line
-        reset_lnbuff();
-        return c;
+    if (c == EOF || c == '\n') // new line
+        lnbuff.len = 0;
+    else {
+        lnbuff.self[LNBUFF_I] = c;
+        lnbuff.len++;
     }
 
-    if (lnbuff.trunc) 
-        lnbuff.trunc++;
-    
-    if (lnbuff.i == LNBUFF_LEN) {
-        lnbuff.i = 0;
-        if (!lnbuff.trunc)
-            lnbuff.trunc = 1;
-    }
-
-    lnbuff.self[lnbuff.i++] = c;
     return c;
 }
 
 /* flush_lnbuff: print contents of line buffer, return length */
 int flush_lnbuff()
 {
-    int i, len = lnbuff.i;
+    int i;
 
-    if (lnbuff.trunc) {
-        len = LNBUFF_LEN + lnbuff.trunc;
-        for (i = 0; i < lnbuff.trunc; i++)
+    /* handle overflowing chars */
+    if (lnbuff.len > LNBUFF_LEN) {
+        for (i = LNBUFF_LEN; i < lnbuff.len; i++)
             putchar('.');
-        for (i = lnbuff.i; i < LNBUFF_LEN; i++)
+        for (i = LNBUFF_I; i < LNBUFF_LEN; i++)
             putchar(lnbuff.self[i]);
     }
-    for (i = 0; i < lnbuff.i; i++)
+    /* handle rest of chars */
+    for (i = 0; i < LNBUFF_I; i++)
         putchar(lnbuff.self[i]);
-    reset_lnbuff();
-    return len;
+
+    i = lnbuff.len;
+    lnbuff.len = 0;
+    return i;
 }