[wiki] [sites] Improve the invert.c example || FRIGN

[git]

commit 394133dbfc215bb86f80c9419f54d119b009178f
Author: FRIGN <d...@frign.de>
Date:   Tue Mar 15 09:37:48 2016 +0100

    Improve the invert.c example
    
    Use the best practices(tm) inherited from the codebase. This brings
    around 75% speed improvement.
    Also avoid unaligned memory accesses while reading the header by reading
    in uint32_t instead of uint8_t.

diff --git a/tools.suckless.org/farbfeld/invert.c 
b/tools.suckless.org/farbfeld/invert.c
index 2e6f67a..de6b875 100644
--- a/tools.suckless.org/farbfeld/invert.c
+++ b/tools.suckless.org/farbfeld/invert.c
@@ -12,40 +12,44 @@
 int
 main(int argc, char *argv[])
 {
-       uint32_t width, height, i, j, k;
-       uint16_t rgba[4];
-       uint8_t hdr[strlen("farbfeld") + 2 * sizeof(uint32_t)];
+       uint64_t rowlen;
+       uint32_t hdr[4], width, height, i, j;
+       uint16_t *row, *rgba;
 
        if (argc > 1) {
                fprintf(stderr, "usage: %s
", argv[0]);
                return 1;
        }
 
-       if (fread(hdr, 1, sizeof(hdr), stdin) != sizeof(hdr)) {
-               fprintf(stderr, "incomplete header
");
+       if (fread(hdr, sizeof(uint32_t), 4, stdin) != 4) {
+               fprintf(stderr, "%s: fread error
", argv[0]);
                return 1;
        }
-       if (memcmp("farbfeld", hdr, strlen("farbfeld"))) {
-               fprintf(stderr, "invalid magic
");
+       if (memcmp("farbfeld", hdr, sizeof("farbfeld") - 1)) {
+               fprintf(stderr, "%s: invalid magic value
", argv[0]);
                return 1;
        }
-       width = ntohl(*((uint32_t *)(hdr + 8)));
-       height = ntohl(*((uint32_t *)(hdr + 12)));
+       width = ntohl(hdr[2]);
+       height = ntohl(hdr[3]);
 
-       if (fwrite(hdr, 1, sizeof(hdr), stdout) != sizeof(hdr)) {
-               fprintf(stderr, "write error
");
+       if (fwrite(hdr, sizeof(uint32_t), 4, stdout) != 4) {
+               fprintf(stderr, "%s: fwrite error
", argv[0]);
                return 1;
        }
 
+       rowlen = (sizeof("RGBA") - 1) * width;
+       if (!(row = malloc(rowlen * sizeof(uint16_t)))) {
+               fprintf(stderr, "%s: malloc: out of memory
", argv[0]);
+               return 1;
+       }
        for (i = 0; i < height; i++) {
-               for (j = 0; j < width; j++) {
-                       if (fread(rgba, sizeof(uint16_t), 4,
-                                 stdin) != 4) {
-                               fprintf(stderr, "unexpected EOF
");
-                               return 1;
-                       }
-                       for (k = 0; k < 4; k++) {
-                               rgba[k] = ntohs(rgba[k]);
+               if (fread(row, sizeof(uint16_t), rowlen, stdin) != rowlen) {
+                       fprintf(stderr, "%s: fread error
", argv[0]);
+                       return 1;
+               }
+               for (rgba = row; (rgba - row) < rowlen; rgba += 4) {
+                       for (j = 0; j < 4; j++) {
+                               rgba[j] = ntohs(rgba[j]);
                        }
 
                        /* invert colors */
@@ -53,15 +57,14 @@ main(int argc, char *argv[])
                        rgba[1] = 65535 - rgba[1];
                        rgba[2] = 65535 - rgba[2];
 
-                       for (k = 0; k < 4; k++) {
-                               rgba[k] = htons(rgba[k]);
-                       }
-                       if (fwrite(rgba, sizeof(uint16_t), 4,
-                                  stdout) != 4) {
-                               fprintf(stderr, "write error
");
-                               return 1;
+                       for (j = 0; j < 4; j++) {
+                               rgba[j] = htons(rgba[j]);
                        }
                }
+               if (fwrite(row, sizeof(uint16_t), rowlen, stdout) != rowlen) {
+                       fprintf(stderr, "%s: fwrite error
", argv[0]);
+                       return 1;
+               }
        }
 
        return 0;