Changeset e3a9733 in sasmodels

Timestamp:

Dec 23, 2015 10:05:05 AM (9 years ago)

Author:

Paul Kienzle <pkienzle@…>

Branches:

master, core_shell_microgels, costrafo411, magnetic_model, release_v0.94, release_v0.95, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests

Children:

cde11f0f

Parents:

644430f

Message:

support kahan summation to avoid roundoff error, but don't turn it on

File:

• sasmodels/kernel_template.c (modified) (3 diffs)

sasmodels/kernel_template.c

@@ -5 +5 @@
 # define USE_OPENCL
 #endif
+
+#define USE_KAHAN_SUMMATION 0
 
 // If opencl is not available, then we are compiling a C function
@@ -185 +187 @@
     const double qxi = qx[i];
     const double qyi = qy[i];
+    #if USE_KAHAN_SUMMATION
+    double accumulated_error = 0.0;
+    #endif
 #ifdef IQXY_OPEN_LOOPS
     double ret=0.0, norm=0.0;
@@ -207 +212 @@
         // rather than theta in this correction.  Current code uses cos(theta)
         // so that values match those of sasview.
-      #ifdef IQXY_HAS_THETA
+      #if defined(IQXY_HAS_THETA) // && 0
         const double spherical_correction
-          = (Ntheta>1 ? fabs(cos(M_PI_180*theta))*M_PI_2:1.0);
-        ret += spherical_correction * weight * scattering;
+          = (Ntheta>1 ? fabs(cos(M_PI_180*phi))*M_PI_2:1.0);
+        const double next = spherical_correction * weight * scattering;
       #else
-        ret += weight * scattering;
+        const double next = weight * scattering;
+      #endif
+      #if USE_KAHAN_SUMMATION
+        const double y = next - accumulated_error;
+        const double t = ret + y;
+        accumulated_error = (t - ret) - y;
+        ret = t;
+      #else
+        ret += next;
       #endif
         norm += weight;