From 95fcf53353c4205cc75fe6e63752bccc34dda231 Mon Sep 17 00:00:00 2001
From: Seth Hillbrand <seth@kipro-pcb.com>
Date: Thu, 7 Jul 2022 10:53:06 -0700
Subject: [PATCH] Handle basic rounding error in schematic import

The fractional part of Altium schematic units is an integer number of
1/10000 mil segments, which is 2.54 nm.  The internal unit of eeschema
is 10 nm, so each fractional unit in Altium is 0.254 base eeschema
units.  To be consistent with
https://gitlab.com/kicad/code/kicad/-/commit/cf33cfcad1ce01d866548c4ef87a1125141d427b
we round to the nearest 10nm for each element

Fixes https://gitlab.com/kicad/code/kicad/issues/11742

(cherry picked from commit 6fef054c51488878b4d4ec4e1c6852c4643fec43)
---
 eeschema/sch_plugins/altium/altium_parser_sch.cpp | 7 ++++++-
 libs/kimath/include/math/util.h                   | 2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/eeschema/sch_plugins/altium/altium_parser_sch.cpp b/eeschema/sch_plugins/altium/altium_parser_sch.cpp
index 2978608cfb..bac7716792 100644
--- a/eeschema/sch_plugins/altium/altium_parser_sch.cpp
+++ b/eeschema/sch_plugins/altium/altium_parser_sch.cpp
@@ -43,7 +43,12 @@ ALTIUM_SCH_RECORD ReadRecord( const std::map<wxString, wxString>& aProps )
 
 constexpr int Altium2KiCadUnit( const int val, const int frac )
 {
-    return Mils2iu( val ) * 10 + Mils2iu( frac ) / 10000; // TODO: correct, rounding issues?
+    constexpr double int_limit = ( std::numeric_limits<int>::max() - 10 ) / 2.54;
+
+    double dbase = 10 * Mils2iu( val );
+    double dfrac = Mils2iu( frac ) / 10000.0;
+
+    return KiROUND( Clamp<double>( -int_limit, ( dbase + dfrac ) / 10.0, int_limit ) ) * 10;
 }
 
 
diff --git a/libs/kimath/include/math/util.h b/libs/kimath/include/math/util.h
index c9407c2086..d6e9fab913 100644
--- a/libs/kimath/include/math/util.h
+++ b/libs/kimath/include/math/util.h
@@ -49,7 +49,7 @@ void kimathLogDebug( const char* aFormatString, ... );
  * result is:  lower <= value <= upper
  *</p>
  */
-template <typename T> inline const T& Clamp( const T& lower, const T& value, const T& upper )
+template <typename T> inline constexpr T Clamp( const T& lower, const T& value, const T& upper )
 {
     if( value < lower )
         return lower;