Optimized decimal and hex string parsing in hot path.

Using specialized and inline-able parsers instead of strtoul() improved
pixel throughput from ~63MB/s to ~83MB/s (+30%) on a single core
on my machine.

As a side effect, the PX command now allows any non-decimal
character as separator between parameters ¯\_(ツ)_/¯

pixelnuke/Makefile

@@ -1,15 +1,16 @@
 .PHONY: default all clean
 
 CC = gcc
-CFLAGS = -Wall -pthread -O2
+CFLAGS = -Wall -pthread
 LIBS = -levent -levent_pthreads -lrt -lGL -lGLEW -lglfw
 TARGET = pixelnuke
 
+default: CFLAGS += -O2 -flto
 default: $(TARGET)
 all: default
 
 debug: CFLAGS += -DDEBUG -g
-debug: default
+debug: $(TARGET)
 
 OBJECTS = $(patsubst %.c, %.o, $(wildcard *.c))
 HEADERS = $(wildcard *.h)

pixelnuke/pixelnuke.c

@@ -10,9 +10,14 @@ unsigned int px_height = 1024;
 unsigned int px_pixelcount = 0;
 unsigned int px_clientcount = 0;
 
+// User sessions
+typedef struct PxSession {
+
+} PxSession;
+
 // Helper functions
 
-static int util_str_starts_with(const char* prefix, const char* str) {
+static inline int fast_str_startswith(const char* prefix, const char* str) {
 	char cp, cs;
 	while ((cp = *prefix++) == (cs = *str++)) {
 		if (cp == 0)
@@ -21,39 +26,71 @@ static int util_str_starts_with(const char* prefix, const char* str) {
 	return !cp;
 }
 
+// Decimal string to unsigned int. This variant does NOT consume +, - or whitespace.
+// If **endptr is not NULL, it will point to the first non-decimal character, which
+// may be \0 at the end of the string.
+static inline uint32_t fast_strtoul10(const char *str, const char **endptr) {
+	uint32_t result = 0;
+	unsigned char c;
+	for (; (c = *str - '0') <= 9; str++)
+		result = result * 10 + c;
+	if (endptr)
+		*endptr = str;
+	return result;
+}
+
+// Same as fast_strtoul10, but for hex strings.
+static inline uint32_t fast_strtoul16(const char *str, const char **endptr) {
+	uint32_t result = 0;
+	unsigned char c;
+	while ((c = *str - '0') <= 9 // 0-9
+			|| ((c -= 7) >= 10 && c <= 15) // A-F
+			|| ((c -= 32) >= 10 && c <= 15)) { // a-f
+		result = result * 16 + c;
+		str++;
+	}
+	if (endptr)
+		*endptr = str;
+	return result;
+}
+
 // server callbacks
 void px_on_connect(NetClient *client) {
 	px_clientcount++;
 }
 
-
 void px_on_close(NetClient *client, int error) {
 	px_clientcount--;
 }
 
-
 void px_on_read(NetClient *client, char *line) {
-	if (util_str_starts_with("PX ", line)) {
+	if (fast_str_startswith("PX ", line)) {
 		const char * ptr = line + 3;
-		char * endptr = (char*) ptr;
+		const char * endptr = ptr;
 		errno = 0;
 
-		unsigned int x = strtoul(ptr, &endptr, 10);
-		if (endptr == ptr || errno) {
+		uint32_t x = fast_strtoul10(ptr, &endptr);
+		if (endptr == ptr) {
 			net_err(client,
-					"First parameter missing or invalid (should be decimal)");
+					"Invalid command (expected decimal as first parameter)");
+			return;
+		}
+		if (*endptr == '\0') {
+			net_err(client, "Invalid command (second parameter required)");
 			return;
 		}
 
-		unsigned int y = strtoul((ptr = endptr), &endptr, 10);
-		if (endptr == ptr || errno) {
+		endptr++; // eat space (or whatever non-decimal is found here)
+
+		uint32_t y = fast_strtoul10((ptr = endptr), &endptr);
+		if (endptr == ptr) {
 			net_err(client,
-					"Second parameter missing or invalid (should be decimal)");
+					"Invalid command (expected decimal as second parameter)");
 			return;
 		}
 
 		// PX <x> <y> -> Get RGB color at position (x,y) or '0x000000' for out-of-range queries
-		if (*endptr == 0) {
+		if (*endptr == '\0') {
 			uint32_t c;
 			canvas_get_px(x, y, &c);
 			char str[64];
@@ -62,20 +99,22 @@ void px_on_read(NetClient *client, char *line) {
 			return;
 		}
 
+		endptr++; // eat space (or whatever non-decimal is found here)
+
 		// PX <x> <y> BB|RRGGBB|RRGGBBAA
-		unsigned long int c = strtoul((ptr = endptr), &endptr, 16);
-		if (endptr == ptr || errno) {
+		uint32_t c = fast_strtoul16((ptr = endptr), &endptr);
+		if (endptr == ptr) {
 			net_err(client,
 					"Third parameter missing or invalid (should be hex color)");
 			return;
 		}
 
-		if (endptr - 1 - 6 == ptr) {
-			// RGB -> RGBA
+		if (endptr - ptr == 6) {
+			// RGB -> RGBA (most common)
 			c = (c << 8) + 0xff;
-		} else if (endptr - 1 - 8 == ptr) {
+		} else if (endptr - ptr == 8) {
 			// done
-		} else if (endptr - 1 - 2 == ptr) {
+		} else if (endptr - ptr == 2) {
 			// WW -> RGBA
 			c = (c << 24) + (c << 16) + (c << 8) + 0xff;
 		} else {
@@ -87,22 +126,23 @@ void px_on_read(NetClient *client, char *line) {
 		px_pixelcount++;
 		canvas_set_px(x, y, c);
 
-	} else if (util_str_starts_with("SIZE", line)) {
+	} else if (fast_str_startswith("SIZE", line)) {
 
 		char str[64];
 		snprintf(str, 64, "SIZE %d %d", px_width, px_height);
 		net_send(client, str);
 
-	} else if (util_str_starts_with("STATS", line)) {
+	} else if (fast_str_startswith("STATS", line)) {
 
 		char str[128];
-		snprintf(str, 128, "STATS px:%u conn:%u", px_pixelcount, px_clientcount);
+		snprintf(str, 128, "STATS px:%u conn:%u", px_pixelcount,
+				px_clientcount);
 		net_send(client, str);
 
-	} else if (util_str_starts_with("HELP", line)) {
+	} else if (fast_str_startswith("HELP", line)) {
 
 		net_send(client,
-"\
+				"\
 PX x y: Get color at position (x,y)\n\
 PX x y rrggbb(aa): Draw a pixel (with optional alpha channel)\n\
 SIZE: Get canvas size\n\
@@ -115,7 +155,6 @@ STATS: Return statistics");
 	}
 }
 
-
 void px_on_key(int key, int scancode, int mods) {
 
 	printf("Key pressed: key:%d scancode:%d mods:%d\n", key, scancode, mods);