[hackers] [dmenu][PATCH] minor improvement to the nomatches cache

From: NRK <nrk_AT_disroot.org>
Date: Thu, 6 Jul 2023 20:42:00 +0600

1. use `unsigned int` to store the codepoints, this avoids waste on
   common case where `long` is 64bits. and POSIX guarantees `int` to be
   at least 32bits so there's no risk of truncation.
2. since switching to `unsigned int` cuts down the memory requirement by
   half, double the cache size from 64 to 128.
3. instead of a linear search, use a simple hash-table for O(1) lookups.

---
 dmenu.c |  1 -
 drw.c   | 22 +++++++++++-----------
 util.h  |  1 +
 3 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/dmenu.c b/dmenu.c
index 62f1089..40f93e0 100644
--- a/dmenu.c
+++ b/dmenu.c
_AT_@ -22,7 +22,6 @@
 /* macros */
 #define INTERSECT(x,y,w,h,r)  (MAX(0, MIN((x)+(w),(r).x_org+(r).width)  - MAX((x),(r).x_org)) \
                              * MAX(0, MIN((y)+(h),(r).y_org+(r).height) - MAX((y),(r).y_org)))
-#define LENGTH(X)             (sizeof X / sizeof X[0])
 #define TEXTW(X)              (drw_fontset_getwidth(drw, (X)) + lrpad)
 
 /* enums */
diff --git a/drw.c b/drw.c
index a58a2b4..00a6112 100644
--- a/drw.c
+++ b/drw.c
_AT_@ -238,8 +238,8 @@ drw_rect(Drw *drw, int x, int y, unsigned int w, unsigned int h, int filled, int
 int
 drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lpad, const char *text, int invert)
 {
-	int i, ty, ellipsis_x = 0;
-	unsigned int tmpw, ew, ellipsis_w = 0, ellipsis_len;
+	int ty, ellipsis_x = 0;
+	unsigned int tmpw, ew, ellipsis_w = 0, ellipsis_len, hash;
 	XftDraw *d = NULL;
 	Fnt *usedfont, *curfont, *nextfont;
 	int utf8strlen, utf8charlen, render = x || y || w || h;
_AT_@ -251,9 +251,7 @@ drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lp
 	XftResult result;
 	int charexists = 0, overflow = 0;
 	/* keep track of a couple codepoints for which we have no match. */
-	enum { nomatches_len = 64 };
-	static struct { long codepoint[nomatches_len]; unsigned int idx; } nomatches;
-	static unsigned int ellipsis_width = 0;
+	static unsigned int nomatches[128], ellipsis_width;
 
 	if (!drw || (render && (!drw->scheme || !w)) || !text || !drw->fonts)
 		return 0;
_AT_@ -338,11 +336,13 @@ drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lp
 			 * character must be drawn. */
 			charexists = 1;
 
-			for (i = 0; i < nomatches_len; ++i) {
-				/* avoid calling XftFontMatch if we know we won't find a match */
-				if (utf8codepoint == nomatches.codepoint[i])
-					goto no_match;
-			}
+			hash = (unsigned int)utf8codepoint;
+			hash = ((hash >> 16) ^ hash) * 0x21F0AAAD;
+			hash = ((hash >> 15) ^ hash) * 0xD35A2D97;
+			hash = ((hash >> 15) ^ hash) % LENGTH(nomatches);
+			/* avoid expensive XftFontMatch call when we know we won't find a match */
+			if (nomatches[hash] == utf8codepoint)
+				goto no_match;
 
 			fccharset = FcCharSetCreate();
 			FcCharSetAddChar(fccharset, utf8codepoint);
_AT_@ -371,7 +371,7 @@ drw_text(Drw *drw, int x, int y, unsigned int w, unsigned int h, unsigned int lp
 					curfont->next = usedfont;
 				} else {
 					xfont_free(usedfont);
-					nomatches.codepoint[++nomatches.idx % nomatches_len] = utf8codepoint;
+					nomatches[hash] = utf8codepoint;
 no_match:
 					usedfont = drw->fonts;
 				}
diff --git a/util.h b/util.h
index f633b51..c0a50d4 100644
--- a/util.h
+++ b/util.h
_AT_@ -3,6 +3,7 @@
 #define MAX(A, B)               ((A) > (B) ? (A) : (B))
 #define MIN(A, B)               ((A) < (B) ? (A) : (B))
 #define BETWEEN(X, A, B)        ((A) <= (X) && (X) <= (B))
+#define LENGTH(X)               (sizeof (X) / sizeof (X)[0])
 
 void die(const char *fmt, ...);
 void *ecalloc(size_t nmemb, size_t size);
-- 
2.41.0

Received on Thu Jul 06 2023 - 16:42:00 CEST