From 221c040ec2848a388879f175d88094769fe14c74 Mon Sep 17 00:00:00 2001
From: MetalliC <0vetal0@gmail.com>
Date: Fri, 20 Sep 2019 18:40:27 +0300
Subject: [PATCH] cps3.cpp: replaced color DMA fading algo, expected to be
 hardware-accurate

---
 src/mame/drivers/cps3.cpp | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/src/mame/drivers/cps3.cpp b/src/mame/drivers/cps3.cpp
index c5a671e89cb..44b6fe3bacc 100644
--- a/src/mame/drivers/cps3.cpp
+++ b/src/mame/drivers/cps3.cpp
@@ -937,16 +937,12 @@ static const gfx_layout cps3_tiles8x8_layout =
 
 static inline u8 get_fade(int c, int f)
 {
-	// bit 7 unknown
+	// bit 7 unused, explicit masked out
 	// bit 6 fade enable / disable
-	// bit 5 fade mode
+	// bit 5 fade mode (1 = invert input values and output)
 	// bit 4-0 fade value
 	if (f & 0x40) // Fading enable / disable
-	{
-		f &= 0x3f;
-		c = (f & 0x20) ? (c + (((0x1f - c) * (f & 0x1f)) / 0x1f)) : ((c * f) / 0x1f);
-		c = std::max(0, std::min(0x1f, c));
-	}
+		c = (f & 0x20) ? ((((c ^ 0x1f) * (~f & 0x1f)) >> 5) ^ 0x1f) : (c * (f & 0x1f) >> 5);
 	return c;
 }
 
@@ -959,8 +955,6 @@ void cps3_state::set_mame_colours(int colournum, u16 data, u32 fadeval)
 	/* is this 100% correct? */
 	if (fadeval & 0x40400040)
 	{
-		//logerror("fadeval %08x\n",fadeval);
-
 		r = get_fade(r, (fadeval & 0x7f000000)>>24);
 		g = get_fade(g, (fadeval & 0x007f0000)>>16);
 		b = get_fade(b, (fadeval & 0x0000007f)>>0);