random-image-v33.patch

From 7383a00cf4cb2e5011ff9060465616c97d2044ac Mon Sep 17 00:00:00 2001
From: NRK <nrk@disroot.org>
Date: Tue, 11 Feb 2025 14:15:03 +0000
Subject: [PATCH] add keybind to switch to random image

---
 commands.c   | 32 ++++++++++++++++++++++++++++++++
 commands.h   |  2 ++
 config.def.h |  1 +
 main.c       |  1 +
 4 files changed, 36 insertions(+)

diff --git a/commands.c b/commands.c
index 3257b1e..672f74a 100644
--- a/commands.c
+++ b/commands.c
@@ -477,3 +477,35 @@ bool ct_select(arg_t _)
 
 	return dirty;
 }
+
+/*
+ * NOTE(NRK): could be faster with __builtin_clz(), but i've opted for portibility instead.
+ * ref: https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+ */
+static unsigned int next_power_of_2_modmask(unsigned int v)
+{
+	--v;
+	v |= v >> 1;
+	v |= v >> 2;
+	v |= v >> 4;
+	v |= v >> 8;
+	v |= v >> 16;
+	return v;
+}
+
+/*
+ * rejects any baised samples with the bitmask approach described in:
+ * https://www.pcg-random.org/posts/bounded-rands.html
+ */
+bool cg_random(arg_t _)
+{
+	if (filecnt >= 2) {
+		int n;
+		unsigned int mask = next_power_of_2_modmask(filecnt);
+		do {
+			n = rand() & mask;
+		} while (n >= filecnt || n == fileidx);
+		return navigate_to(n);
+	}
+	return false;
+}
diff --git a/commands.h b/commands.h
index 4e694f0..10b5008 100644
--- a/commands.h
+++ b/commands.h
@@ -23,6 +23,7 @@ bool cg_toggle_fullscreen(arg_t);
 bool cg_toggle_image_mark(arg_t);
 bool cg_unmark_all(arg_t);
 bool cg_zoom(arg_t);
+bool cg_random(arg_t);
 /* image mode */
 bool ci_alternate(arg_t);
 bool ci_cursor_navigate(arg_t);
@@ -69,6 +70,7 @@ bool ct_select(arg_t);
 #define g_toggle_image_mark { cg_toggle_image_mark, MODE_ALL }
 #define g_unmark_all { cg_unmark_all, MODE_ALL }
 #define g_zoom { cg_zoom, MODE_ALL }
+#define g_random { cg_random, MODE_ALL }
 
 /* image mode */
 #define i_alternate { ci_alternate, MODE_IMAGE }
diff --git a/config.def.h b/config.def.h
index ead1509..1d4d0f4 100644
--- a/config.def.h
+++ b/config.def.h
@@ -107,6 +107,7 @@ static const keymap_t keys[] = {
 	{ ControlMask,  XK_x,             g_prefix_external,    None },
 	{ 0,            XK_g,             g_first,              None },
 	{ 0,            XK_G,             g_n_or_last,          None },
+	{ ControlMask,  XK_r,             g_random,             None },
 	{ 0,            XK_r,             g_reload_image,       None },
 	{ 0,            XK_D,             g_remove_image,       None },
 	{ ControlMask,  XK_h,             g_scroll_screen,      DIR_LEFT },
diff --git a/main.c b/main.c
index 6ca2f11..9dba4c2 100644
--- a/main.c
+++ b/main.c
@@ -901,6 +901,7 @@ int main(int argc, char *argv[])
 	setup_signal(SIGCHLD, SIG_DFL, SA_RESTART | SA_NOCLDSTOP | SA_NOCLDWAIT);
 	setup_signal(SIGPIPE, SIG_IGN, 0);
 
+	srand(time(NULL));
 	setlocale(LC_COLLATE, "");
 
 	parse_options(argc, argv);
-- 
2.46.2