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diff Discovery/Src/buehlmann.c @ 250:822416168585 bm-2

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Buelmann: new implementation for ceiling Since my first functional fix in the ceiling computation in commit ceecabfddb57, I noticed that the computation used a linear search, that became rather computational expensive after that commit. The simple question is: why not a binary search? So, this commit implements the binary search. But there is a long story attached to this. Comparing ceiling results from hwOS and this OSTC4 code were very different. Basically, the original OSTC4 algorithm computed the ceiling using the same GFlow to GFhigh slope, in such a way, that the ceiling was in sync with the presented deco stops, where the hwOS code presents a GFhigh based ceiling. This said, it is more logical when the OSTC4 and hwOS code give similar results. This new recursive algorithm gives very similar results for the ceiling compared to hwOS. To be complete here, the Buelmann ceiling is the depth to which you can ascend, so that the leading tissue reaches GFhigh. This also explains why the deepest deco stop is normally deeper than the ceiling (unless one dives with GF like 80/80). The code implemented here is rather straightforward recursion. Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>
author Jan Mulder <jlmulder@xs4all.nl>
date Thu, 11 Apr 2019 17:48:48 +0200
parents 3949781096d4
children 1663b3b204d7
line wrap: on
line diff
--- a/Discovery/Src/buehlmann.c	Thu Apr 11 10:26:22 2019 +0000
+++ b/Discovery/Src/buehlmann.c	Thu Apr 11 17:48:48 2019 +0200
@@ -67,7 +67,6 @@
 float get_gf_at_pressure(float pressure);
 void buehlmann_calc_ndl(void);
 _Bool dive1_check_deco(void);
-uint8_t buehlmann_tissue_test_tolerance(float depth_in_bar_absolute);
 
 /*
 _____________________________________________________________
@@ -446,7 +445,7 @@
 }
 
 
-uint8_t buehlmann_tissue_test_tolerance(float depth_in_bar_absolute)
+float buehlmann_tissue_test_tolerance(float depth_in_bar_absolute)
 {
 	float tissue_inertgas_saturation;
 	float inertgas_a;
@@ -461,24 +460,20 @@
 		if(gTissue_helium_bar[ci] == 0)
 		{
 			tissue_inertgas_saturation = gTissue_nitrogen_bar[ci];
-			//
 			inertgas_a = buehlmann_N2_a[ci];
 			inertgas_b = buehlmann_N2_b[ci];
 		}
 		else
 		{
 			tissue_inertgas_saturation =  gTissue_nitrogen_bar[ci] + gTissue_helium_bar[ci];
-			//
 			inertgas_a = ( ( buehlmann_N2_a[ci] *  gTissue_nitrogen_bar[ci]) + ( buehlmann_He_a[ci] * gTissue_helium_bar[ci]) ) / tissue_inertgas_saturation;
 			inertgas_b = ( ( buehlmann_N2_b[ci] *  gTissue_nitrogen_bar[ci]) + ( buehlmann_He_b[ci] * gTissue_helium_bar[ci]) ) / tissue_inertgas_saturation;
 		}
-		//
 		inertgas_tolerance = ( (gGF_value / inertgas_b - gf_minus_1) * depth_in_bar_absolute ) + ( gGF_value * inertgas_a );
-		//
 		if(inertgas_tolerance < tissue_inertgas_saturation)
-			return 0;
+			return tissue_inertgas_saturation - inertgas_tolerance; // positive
 	}
-	return 1;
+	return tissue_inertgas_saturation - inertgas_tolerance; // negative
 }
 
 
@@ -715,74 +710,37 @@
 		return true;
 }
 
-
-void buehlmann_ceiling_calculator(SLifeData* pLifeData, SDiveSettings * pDiveSettings, SDecoinfo * pDecoInfo)
+// compute ceiling recursively, with a resolution of 10cm. Notice
+// that the initial call shall guarantee that the found ceiling
+// is between low and high parameters.
+static float compute_ceiling(float low, float high)
 {
-	float gf_low;
-	float gf_high;
-	float gf_delta;
-	float dv_gf_low_stop_meter;
-	_Bool test_result;
-	float next_gf_value;
-	float next_pressure_absolute;
-	float depth_in_meter;
-	
-	gf_low = pDiveSettings->gf_low;
-	gf_high = pDiveSettings->gf_high;
+	if ((high - low) < 0.01)
+		return low;
+	else {
+		float next_pressure_absolute = (low + high)/2;
+		float test_result = buehlmann_tissue_test_tolerance(next_pressure_absolute);
+		if (test_result < 0)
+			return compute_ceiling(low, next_pressure_absolute);
+		else
+			return compute_ceiling(next_pressure_absolute, high);
+	}
+}
 
-	dv_gf_low_stop_meter = (int)((pDiveSettings->internal__pressure_first_stop_ambient_bar_as_upper_limit_for_gf_low_otherwise_zero - pLifeData->pressure_surface_bar) * 10);
+void buehlmann_ceiling_calculator(SLifeData *pLifeData, SDecoinfo *pDecoInfo)
+{
+	float ceiling;
 
-	if(dv_gf_low_stop_meter < 1)
-	{
-		next_gf_value = gf_high; // fix hw 161024
-		gf_delta = 0;
+	// this is just performance optimizing. The code below runs just fine
+	// without this. There is never a ceiling in NDL deco state
+	if (!pDecoInfo->output_time_to_surface_seconds) {
+		pDecoInfo->output_ceiling_meter = 0;
+		return;
 	}
-	else
-	{
-		next_gf_value = gf_high;
-		gf_delta = gf_high - gf_low;
-		gf_delta /= (dv_gf_low_stop_meter * 10); // gf_delta is delta for 10 cm !!
-	}
-
-	depth_in_meter = 0;
-	next_pressure_absolute = pLifeData->pressure_surface_bar;
 
 	memcpy(gTissue_nitrogen_bar, pLifeData->tissue_nitrogen_bar, (4*16));
 	memcpy(gTissue_helium_bar, pLifeData->tissue_helium_bar, (4*16));
-	gGF_value = next_gf_value / 100.0f;
-	//
-	test_result = buehlmann_tissue_test_tolerance(next_pressure_absolute);
-	//
-	while(!test_result && depth_in_meter < 200)
-	{
-		depth_in_meter += 0.1;
-		next_gf_value = fmaxf(gf_low, next_gf_value - gf_delta);
-		gGF_value = next_gf_value / 100.0f;
-		next_pressure_absolute += 0.01f; // 0.1 meter down
-		test_result = buehlmann_tissue_test_tolerance(next_pressure_absolute);
-	}
 
-	if(test_result)
-	{
-		pDecoInfo->output_ceiling_meter = depth_in_meter;
-
-		if(depth_in_meter >= 0)
-		{
-			for(int i = 0; i < 10; i++)
-			{
-				next_gf_value += gf_delta/10.0f;
-				gGF_value = next_gf_value / 100.0f;
-				next_pressure_absolute -= 0.01f; // 0.1 meter up
-				if(!buehlmann_tissue_test_tolerance(next_pressure_absolute))
-				{
-					pDecoInfo->output_ceiling_meter -= ((float)i)/10.0f;
-					break;
-				}
-			}
-		}
-	}
-	else
-	{
-		pDecoInfo->output_ceiling_meter = 999;
-	}
+	ceiling = compute_ceiling(pLifeData->pressure_surface_bar, 1.0f + pLifeData->max_depth_meter/10.0f);
+	pDecoInfo->output_ceiling_meter = (ceiling - pLifeData->pressure_surface_bar) * 10.0f;
 }