Index: openacs-4/packages/accounts-finance/tcl/math-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/accounts-finance/tcl/math-procs.tcl,v
diff -u -N -r1.1 -r1.2
--- openacs-4/packages/accounts-finance/tcl/math-procs.tcl	15 Jun 2012 22:24:45 -0000	1.1
+++ openacs-4/packages/accounts-finance/tcl/math-procs.tcl	14 Nov 2014 18:20:17 -0000	1.2
@@ -7,28 +7,58 @@
 
 namespace eval acc_fin {}
 
-ad_proc -public interpolatep1p2_at_x {
+ad_proc -public qaf_interpolatep1p2_at_x {
     p1_x
-    P1_y
+    p1_y
     p2_x
     p2_y
     p3_x
+    {avg_p "0"}
 } {
-    returns y value of third point (p3), given cartesion points p1(x,y), p2(x,y)
+    returns y value of third point (p3), given cartesion points p1(x,y), p2(x,y). if avg_p == 1, returns the average of p1_y and p2_y instead of returning an empty string. 
+    The average is useful for some point interpretations.
 } {
     # interpolate, y=mx+b, slope = Dy/Dx = m, b = y axis intercept
     if { $p2_x != $p1_x } {
+        # Classic math way:
         set m [expr { ($p2_y - $p1_y) / ($p2_x - $p1_x) }]
         if { $p2_x != 0 } {
             set b [expr { $p2_y / ( $m * $p2_x ) } ]
         } else { $p1_y != 0 } {
             set b [expr { $p1_y / ( $m * $p1_x ) } ]
         }
         set p3_y [expr { ( $m * $p3_x ) + $b } ]
+# This might work, but haven't completely tested.. would be faster if it does.
+#        set delta_x31_pct [expr { ( $p3_x - $p1_x ) / ( $p2_x - $p1_x ) } ]
+#        set p3_y [expr { $delta_x31_pct * ( $p2_y - $p1_y ) } ]
     } else {
         # vertical line. 
-        set p3_y ""
+        if { $avg_p } {
+            set p3_y [expr { ( $p1_y + $p2_y ) / 2. } ]
+        } else {
+            set p3_y ""
+        }
     }
     return $p3_y
 }
- 
\ No newline at end of file
+
+ad_proc -public qaf_round_to_decimals {
+    number
+    {exponent "0"}
+} {
+    Rounds a number to n decimal places.
+} {
+    set magnitude [expr { pow( 10. , $exponent ) } ] 
+    set rounded [expr { round( $number * $magnitude ) / $magnitude } ]
+    return $rounded
+}
+
+ad_proc -public qaf_round_to_precision {
+    number
+    {precision "1"}
+} {
+    Rounds a number to a precision value. This is handy especially for exact monetary change when the smallest unit is not decimal, 0.05 for example.
+} {
+    # copy of dt_round_to_precision from acs-datetime
+    return [expr { $precision * round( double($number) / $precision ) } ]
+}