From c45e1e7f8cbb732586c645fba7e15f58bcc0edcb Mon Sep 17 00:00:00 2001
From: Denis Pauk <pauk.denis@gmail.com>
Date: Tue, 4 Sep 2018 22:51:08 +0300
Subject: [PATCH] correct check for zstep

---
 src/client/refresh/soft/sw_main.c |  2 +-
 src/client/refresh/soft/sw_scan.c | 26 +++++++++++++++++---------
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/client/refresh/soft/sw_main.c b/src/client/refresh/soft/sw_main.c
index d7255745..e98b783f 100644
--- a/src/client/refresh/soft/sw_main.c
+++ b/src/client/refresh/soft/sw_main.c
@@ -833,7 +833,7 @@ Returns an axially aligned box that contains the input box at the given rotation
 =============
 */
 static void
-RotatedBBox (const vec3_t mins, const vec3_t maxs, const vec3_t angles, vec3_t tmins, vec3_t tmaxs)
+RotatedBBox (const vec3_t mins, const vec3_t maxs, vec3_t angles, vec3_t tmins, vec3_t tmaxs)
 {
 	vec3_t	tmp, v;
 	int		i, j;
diff --git a/src/client/refresh/soft/sw_scan.c b/src/client/refresh/soft/sw_scan.c
index 30e82347..017ccc94 100644
--- a/src/client/refresh/soft/sw_scan.c
+++ b/src/client/refresh/soft/sw_scan.c
@@ -144,12 +144,14 @@ D_DrawZSpanGetStepValue(zvalue_t izistep)
 {
 	// check that we can draw parallel surfaces to screen surface
 	// (both ends have same z value)
-	// current step too small to current screen width
-	if (izistep < (SHIFT16XYZ_MULT / vid.width))
-		return vid.width;
+	int	count = 1;
 
-	// look to what is maxumum for current step
-	return SHIFT16XYZ_MULT / izistep;
+	while ((izistep * count) >> SHIFT16XYZ == 0 && count < vid.width)
+	{
+		count <<= 1;
+	}
+
+	return count;
 }
 
 /*
@@ -744,7 +746,7 @@ void
 D_DrawZSpans (espan_t *pspan)
 {
 	zvalue_t	izistep;
-	int	safe_step;
+	int		safe_step;
 
 	// FIXME: check for clamping/range problems
 	// we count on FP exceptions being turned off to avoid range problems
@@ -771,13 +773,19 @@ D_DrawZSpans (espan_t *pspan)
 		// we count on FP exceptions being turned off to avoid range problems
 		izi = (int)(zi * 0x8000 * (float)SHIFT16XYZ_MULT);
 
-		if (safe_step > count)
+		if (safe_step > 1)
 		{
-			zvalue_t izi_shifted = izi >> SHIFT16XYZ;
 			const zvalue_t *tdest_max = pdest + count;
 			do
 			{
-				*pdest++ = izi_shifted;
+				int	step;
+				zvalue_t izi_shifted = izi >> SHIFT16XYZ;
+
+				for(step = 0; (step < safe_step) && (pdest < tdest_max); step++)
+				{
+					*pdest++ = izi_shifted;
+				}
+				izi += (izistep * safe_step);
 			} while (pdest < tdest_max);
 		}
 		else