From 81757c235ff8e112b4baabdd1ff23409426e9c98 Mon Sep 17 00:00:00 2001
From: Philip Wittamore <philip@wittamore.com>
Date: Sun, 8 Jun 2025 22:00:43 +0200
Subject: update

---
 src/timer.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 src/timer.c

(limited to 'src/timer.c')

diff --git a/src/timer.c b/src/timer.c
new file mode 100644
index 0000000..2ee555b
--- /dev/null
+++ b/src/timer.c
@@ -0,0 +1,72 @@
+#include "timer.h"
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "block.h"
+#include "util.h"
+
+static unsigned int compute_tick(const block *const blocks,
+                                 const unsigned short block_count) {
+    unsigned int tick = 0;
+
+    for (unsigned short i = 0; i < block_count; ++i) {
+        const block *const block = &blocks[i];
+        tick = gcd(block->interval, tick);
+    }
+
+    return tick;
+}
+
+static unsigned int compute_reset_value(const block *const blocks,
+                                        const unsigned short block_count) {
+    unsigned int reset_value = 1;
+
+    for (unsigned short i = 0; i < block_count; ++i) {
+        const block *const block = &blocks[i];
+        reset_value = MAX(block->interval, reset_value);
+    }
+
+    return reset_value;
+}
+
+timer timer_new(const block *const blocks, const unsigned short block_count) {
+    const unsigned int reset_value = compute_reset_value(blocks, block_count);
+
+    timer timer = {
+        .time = reset_value,  // Initial value to execute all blocks.
+        .tick = compute_tick(blocks, block_count),
+        .reset_value = reset_value,
+    };
+
+    return timer;
+}
+
+int timer_arm(timer *const timer) {
+    errno = 0;
+    (void)alarm(timer->tick);
+
+    if (errno != 0) {
+        (void)fprintf(stderr, "error: could not arm timer\n");
+        return 1;
+    }
+
+    // Wrap `time` to the interval [1, reset_value].
+    timer->time = (timer->time + timer->tick) % timer->reset_value;
+
+    return 0;
+}
+
+bool timer_must_run_block(const timer *const timer, const block *const block) {
+    if (timer == NULL || timer->time == timer->reset_value) {
+        return true;
+    }
+
+    if (block->interval == 0) {
+        return false;
+    }
+
+    return timer->time % block->interval == 0;
+}
-- 
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