further optimizations

k&r/03-control-flow/03-03.c

@@ -53,8 +53,8 @@ void expand(char *s, char *t, int n)
         CHECK_OVERFLOW(i, n);
         t[i] = *s;
     }
-    terminate:
-        t[i] = '\0';
+terminate:
+    t[i] = '\0';
 }
 
 /* getstr: copies stdin to array s of length n, returns size of string or 

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

@@ -0,0 +1,118 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <assert.h>
+
+int grep(char pattern[]);
+
+/* grep with graceful buffer overflow */
+/* parse and verify arg pattern, pass it to grep */
+int main(int argc, char *argv[])
+{
+    /* verify arg is given */
+    if (argc < 2) {
+        printf("error: excpected pattern\n");
+        return -1;
+    }
+
+    char *pattern = argv[1];
+
+    /* verify pattern */
+    char c;
+    int i;
+    for (i = 0; (c = pattern[i]) != '\0'; i++)
+        if (c == '\n') {
+            printf("error: newline in pattern\n");
+            return -2;
+        }
+
+    int found = grep(pattern);
+    printf("found = %d\n", found);
+    return found;
+}
+
+void println(void);
+int flush_lnbuff(void);
+int getch_lnbuff(void);
+
+/* grep: prints lines containing pattern, returns number of matching lines */
+int grep(char *pattern)
+{
+    int found, i, c;
+    const int plen = strlen(pattern);
+
+    i = found = 0;
+
+    while ((c = getch_lnbuff()) != EOF)
+        if (c != pattern[i])
+            i = 0;
+        else if (++i == plen) { // found match
+            i = 0;
+            found++;
+            flush_lnbuff();
+            println(); 
+        }
+    return found;
+}
+
+/* println: prints next line from stdin
+ * prints newline on EOF */
+void println()
+{
+    int c;
+    while ((c = getchar()) != EOF && c != '\n')
+        putchar(c);
+    putchar(c);
+}
+
+/* ------------------------ 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 len;
+} lnbuff = {.len= 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
+        lnbuff.len = 0;
+    else {
+        lnbuff.self[LNBUFF_I] = c;
+        lnbuff.len++;
+    }
+
+    return c;
+}
+
+/* flush_lnbuff: print contents of line buffer, return length */
+int flush_lnbuff()
+{
+    int 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++)
+            putchar(lnbuff.self[i]);
+    }
+    /* handle rest of chars */
+    for (i = 0; i < LNBUFF_I; i++)
+        putchar(lnbuff.self[i]);
+
+    i = lnbuff.len;
+    lnbuff.len = 0;
+    return i;
+}

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

@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+#define W 80
+#define REPEAT 4000000
+
+int main()
+{
+    int i, j;
+    for (i = 0; i < REPEAT; i++) {
+        for (j = 0; j < W; j++)
+            putchar('y');
+        putchar('\n');
+    }
+    return 0;
+}

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

@@ -0,0 +1,75 @@
+#include <stdio.h>
+#include <string.h>
+
+#define MAXLINE 1000 /* maximum input line length */
+
+int grep(char *pattern);
+
+/* somewhat optimized book version of grep */
+/* find all lines matching pattern */
+int main(int argc, char *argv[])
+{
+    /* verify arg is given */
+    if (argc < 2) {
+        printf("error: excpected pattern\n");
+        return -1;
+    }
+
+    char *pattern = argv[1];
+
+    /* verify pattern */
+    char c;
+    int i;
+    for (i = 0; (c = pattern[i]) != '\0'; i++)
+        if (c == '\n') {
+            printf("error: newline in pattern\n");
+            return -2;
+        }
+
+    int found = grep(pattern);
+    printf("found = %d\n", found);
+    return found;
+}
+
+int getln(char line[], int lim);
+int strindex(char source[], char searchfor[], int slen);
+
+/* grep: prints lines containing pattern, returns number of matching lines */
+int grep(char *pattern)
+{
+    char line[MAXLINE];
+    int found = 0;
+    int slen = strlen(pattern);
+
+    while (getln(line, MAXLINE) > 0)
+        if (strindex(line, pattern, slen) >= 0) {
+            printf("%s", line);
+            found++;
+        }
+    return found;
+}
+
+/* getline: get line (including \n) into s, return length */
+int getln(char *s, int lim)
+{
+    int c, i = 0;
+   
+    while (--lim > 0 && (c = getchar()) != EOF && (s[i++] = c) != '\n')
+        ;
+    s[i] = '\0';
+    return i;
+}
+
+/* strindex: return index of t in s, -1 if none */
+int strindex(char s[], char t[], int slen)
+{
+    int i, j;
+
+    for (i = j = 0; s[i]; i++)
+        if (s[i] != t[j])
+            j = 0;
+        else if (++j == slen) { // found match
+            return i - slen + 1;
+        }
+    return -1;
+}