From c2f3a05d92fb6260d689cb4387631442d308400c Mon Sep 17 00:00:00 2001
From: David Schleef <ds@schleef.org>
Date: Wed, 6 Dec 2000 20:09:14 +0000
Subject: [PATCH] new cascade math function by Frank Mori Hess

---
 comedi/drivers/8253.h | 80 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 77 insertions(+), 3 deletions(-)

diff --git a/comedi/drivers/8253.h b/comedi/drivers/8253.h
index 85073bf2..84a3bfe8 100644
--- a/comedi/drivers/8253.h
+++ b/comedi/drivers/8253.h
@@ -26,7 +26,7 @@
 
 #define i8253_cascade_ns_to_timer i8253_cascade_ns_to_timer_power
 
-static inline void i8253_cascade_ns_to_timer_2div(int i8253_osc_base, unsigned int *d1, unsigned int *d2, unsigned int *nanosec, int round_mode)
+static inline void i8253_cascade_ns_to_timer_2div_old(int i8253_osc_base, unsigned int *d1, unsigned int *d2, unsigned int *nanosec, int round_mode)
 {
 	int divider;
 	int div1, div2;
@@ -68,8 +68,8 @@ static inline void i8253_cascade_ns_to_timer_2div(int i8253_osc_base, unsigned i
 	}
 
 	*nanosec = div1_lub * div2_lub * i8253_osc_base;
-	*d1 = div1_lub;
-	*d2 = div2_lub;
+	*d1 = div1_lub & 0xffff;
+	*d2 = div2_lub & 0xffff;
 	return;
 }
 
@@ -110,5 +110,79 @@ static inline void i8253_cascade_ns_to_timer_power(int i8253_osc_base, unsigned
 }
 
 
+/* this function is meant to replace i8253_cascade_ns_to_timer_2div
+ * (which is completely broken at the moment)
+ */
+static inline void i8253_cascade_ns_to_timer_2div(int i8253_osc_base,
+	unsigned int *d1, unsigned int *d2, unsigned int *nanosec, int round_mode)
+{
+	unsigned int divider;
+	unsigned int div1, div2;
+	unsigned int div1_glb, div2_glb, ns_glb;
+	unsigned int div1_lub, div2_lub, ns_lub;
+	unsigned int ns;
+	unsigned int start;
+	unsigned int ns_low, ns_high;
+
+	divider = *nanosec / i8253_osc_base;
+
+	div1_lub = div2_lub = 0;
+	div1_glb = div2_glb = 0;
+
+	ns_glb = 0;
+	ns_lub = 0xffffffff;
+
+	div2 = 0x10000;
+	start = divider / div2;
+	if(start < 2) start = 2;
+	for (div1 = start; div1 <= divider / div1 + 1; div1++) {
+		for(div2 = divider / div1; div1 * div2 <= divider + div1 + 1; div2++) {
+			ns = i8253_osc_base * div1 * div2;
+			if (ns <= *nanosec && ns > ns_glb) {
+				ns_glb = ns;
+				div1_glb = div1;
+				div2_glb = div2;
+			}
+			if (div2 <= 0x10000) {
+				ns = i8253_osc_base * div1 * div2;
+				if (ns >= *nanosec && ns < ns_lub) {
+					ns_lub = ns;
+					div1_lub = div1;
+					div2_lub = div2;
+				}
+			}
+		}
+	}
+
+	switch (round_mode) {
+	case TRIG_ROUND_NEAREST:
+	default:
+		ns_high = div1_lub * div2_lub * i8253_osc_base;
+		ns_low = div1_glb * div2_glb * i8253_osc_base;
+		if( ns_high - *nanosec < *nanosec - ns_low) {
+			div1 = div1_lub;
+			div2 = div2_lub;
+		} else {
+			div1 = div1_glb;
+			div2 = div2_glb;
+		}
+		break;
+	case TRIG_ROUND_UP:
+		div1 = div1_lub;
+		div2 = div2_lub;
+		break;
+	case TRIG_ROUND_DOWN:
+		div1 = div1_glb;
+		div2 = div2_glb;
+		break;
+	}
+
+	*nanosec = div1 * div2 * i8253_osc_base;
+	*d1 = div1 & 0xffff;
+	*d2 = div2 & 0xffff;
+	return;
+}
+
+
 #endif
 
-- 
2.26.2