From 152b06dc825c9b674b56e469af1028a3f8e58d7f Mon Sep 17 00:00:00 2001
From: Campbell Barton <ideasman42@gmail.com>
Date: Thu, 9 Jun 2011 07:40:30 +0000
Subject: [PATCH] use a better method for finding the precision to use for
 float buttons, about 4x faster to calculate and will show for eg, 0.0108
 rather than 0.01, but 0.0100001 still displays as 0.01.

---
 source/blender/editors/interface/interface.c | 51 +++++++++++++-------
 1 file changed, 33 insertions(+), 18 deletions(-)

diff --git a/source/blender/editors/interface/interface.c b/source/blender/editors/interface/interface.c
index a21122698d9..99b4b68b42d 100644
--- a/source/blender/editors/interface/interface.c
+++ b/source/blender/editors/interface/interface.c
@@ -74,6 +74,9 @@
 #define MENU_ITEM_HEIGHT	20
 #define MENU_SEP_HEIGHT		6
 
+#define PRECISION_FLOAT_MAX 7
+#define PRECISION_FLOAT_MAX_POW 10000000 /* pow(10, PRECISION_FLOAT_MAX)  */
+
 /* 
  * a full doc with API notes can be found in bf-blender/trunk/blender/doc/guides/interface_API.txt
  * 
@@ -463,27 +466,39 @@ static int ui_but_float_precision(uiBut *but, double value)
 	 * _but_, this is only for small values si 10.0001 will not get
 	 * the same treatment */
 	if(value != 0.0 && (value= ABS(value)) < 0.1) {
-		double prec_d= -(log10(value));
-		double prec_d_floor = floor(prec_d + FLT_EPSILON);
-		int test_prec= (int)prec_d_floor;
-
-		/* this check is so 0.00016 from isnt rounded to 0.0001 */
-		if(prec_d - prec_d_floor > FLT_EPSILON) { /* not ending with a .0~001 */
-			/* check if a second decimal place is needed 0.00015 for eg. */
-			if(double_round(value, test_prec + 1) - double_round(value, test_prec + 2) != 0.0) {
-				test_prec += 2;
+		int value_i= (int)((value * PRECISION_FLOAT_MAX_POW) + 0.5);
+		if(value_i != 0) {
+			const int prec_span= 3; /* show: 0.01001, 5 would allow 0.0100001 for eg. */
+			int test_prec;
+			int prec_min= -1;
+			int dec_flag= 0;
+			int i= PRECISION_FLOAT_MAX;
+			while(i && value_i) {
+				if(value_i % 10) {
+					dec_flag |= 1<<i;
+					prec_min= i;
+				}
+				value_i /= 10;
+				i--;
 			}
-			else {
-				test_prec += 1;
-			}
-		}
 
-		if(test_prec > prec && test_prec <= 7) {
-			prec= test_prec;
+			/* even though its a small value, if the second last digit is not 0, use it */
+			test_prec = prec_min;
+
+			dec_flag= (dec_flag >> (prec_min + 1)) & ((1 << prec_span) - 1);
+
+			while(dec_flag) {
+				test_prec++;
+				dec_flag = dec_flag >> 1;
+			}
+
+			if(test_prec > prec) {
+				prec= test_prec;
+			}
 		}
 	}
 
-	CLAMP(prec, 1, 7);
+	CLAMP(prec, 1, PRECISION_FLOAT_MAX);
 
 	return prec;
 }
@@ -1484,8 +1499,8 @@ static void ui_get_but_string_unit(uiBut *but, char *str, int len_max, double va
 	if(scene->unit.scale_length<0.0001f) scene->unit.scale_length= 1.0f; // XXX do_versions
 
 	/* Sanity checks */
-	if(precision>7)		precision= 7;
-	else if(precision==0)	precision= 2;
+	if(precision > PRECISION_FLOAT_MAX)	precision= PRECISION_FLOAT_MAX;
+	else if(precision==0)				precision= 2;
 
 	bUnit_AsString(str, len_max, ui_get_but_scale_unit(but, value), precision, scene->unit.system, unit_type>>16, do_split, pad);
 }