From 11a3d8762a9a24f01369ae2f60749e571627925c Mon Sep 17 00:00:00 2001
From: florian <florian@freepascal.org>
Date: Tue, 9 Jan 2018 20:04:49 +0000
Subject: [PATCH] * patch by J. Gareth Moreton:   - Moved the part that emits
 the CMOV command outside of the if-else block, because it's the same in both
 branches and was just duplicated code.   - Moved a comment about powers of 2
 to be right before the correct if-else block.   - Added a couple of comments
 to explain what the algorithm is doing to obtain the remainder.   - Added
 missing "writeln('ok');" (since 'tmoddiv3.pp' has it) and program header to
 'tmoddiv4.pp'.   - Changed program name from "testfile2" to "tmoddiv3" in
 'tmoddiv3.pp'.

git-svn-id: trunk@37939 -
---
 compiler/x86/nx86mat.pas  | 26 ++++++++++++--------------
 tests/test/cg/tmoddiv3.pp |  2 +-
 tests/test/cg/tmoddiv4.pp |  2 ++
 3 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/compiler/x86/nx86mat.pas b/compiler/x86/nx86mat.pas
index d0b20aa562..473e4991ac 100644
--- a/compiler/x86/nx86mat.pas
+++ b/compiler/x86/nx86mat.pas
@@ -524,9 +524,9 @@ interface
                   end;
               end;
           end
-        { unsigned modulus by a (+/-)power-of-2 constant? }
         else if (nodetype=modn) and (right.nodetype=ordconstn) and not(is_signed(left.resultdef)) then
           begin
+            { unsigned modulus by a (+/-)power-of-2 constant? }
             if isabspowerof2(tordconstnode(right).value,power) then
               begin
                 emit_const_reg(A_AND,opsize,(aint(1) shl power)-1,hreg1);
@@ -554,12 +554,6 @@ interface
                         emit_reg_reg(A_XOR,opsize,location.register,location.register);
                         cg.a_reg_alloc(current_asmdata.CurrAsmList,NR_DEFAULTFLAGS);
                         emit_reg_reg(A_CMP,opsize,hreg2,hreg1);
-
-                        { Emit conditional move that depends on the carry flag }
-                        instr:=TAiCpu.op_reg_reg(A_CMOVcc,opsize,hreg3,location.register);
-                        instr.condition := C_AE;
-                        current_asmdata.CurrAsmList.concat(instr);
-                        cg.a_reg_dealloc(current_asmdata.CurrAsmList,NR_DEFAULTFLAGS);
                       end
                     else
                       begin
@@ -568,14 +562,15 @@ interface
 
                         cg.a_reg_alloc(current_asmdata.CurrAsmList,NR_DEFAULTFLAGS);
                         emit_const_reg(A_CMP,opsize,aint(d),hreg1);
-
-                        { Emit conditional move that depends on the carry flag }
-                        instr:=TAiCpu.op_reg_reg(A_CMOVcc,opsize,hreg3,location.register);
-                        instr.condition := C_AE;
-                        current_asmdata.CurrAsmList.concat(instr);
-                        cg.a_reg_dealloc(current_asmdata.CurrAsmList,NR_DEFAULTFLAGS);
                       end;
 
+                    { Emit conditional move that depends on the carry flag being zero,
+                      that is, the comparison result is above or equal }
+                    instr:=TAiCpu.op_reg_reg(A_CMOVcc,opsize,hreg3,location.register);
+                    instr.condition := C_AE;
+                    current_asmdata.CurrAsmList.concat(instr);
+                    cg.a_reg_dealloc(current_asmdata.CurrAsmList,NR_DEFAULTFLAGS);
+
                     emit_reg_reg(A_ADD,opsize,hreg1,location.register);
                   end
                 else
@@ -600,8 +595,11 @@ interface
                         dec(s);
                       end;
                     if s<>0 then
-                      emit_const_reg(A_SHR,opsize,aint(s),regd);
+                      emit_const_reg(A_SHR,opsize,aint(s),regd); { R/EDX now contains the quotient }
 
+                    { Now multiply the quotient by the original denominator and
+                      subtract the product from the original numerator to get
+                      the remainder. }
                     if (cgsize in [OS_64,OS_S64]) then { Cannot use 64-bit constants in IMUL }
                       begin
                         hreg3:=cg.getintregister(current_asmdata.CurrAsmList,cgsize);
diff --git a/tests/test/cg/tmoddiv3.pp b/tests/test/cg/tmoddiv3.pp
index bfcd59d9d6..4a9360de2c 100644
--- a/tests/test/cg/tmoddiv3.pp
+++ b/tests/test/cg/tmoddiv3.pp
@@ -1,4 +1,4 @@
-program testfile2;
+program tmoddiv3;
 
 const
   TestValues: array[0..9] of LongWord = (500, 1, 0, 995, $7FFFFFFF, $80000000, $80000001, $80000002, $FFFFFFFF, 1000000);
diff --git a/tests/test/cg/tmoddiv4.pp b/tests/test/cg/tmoddiv4.pp
index 3ad24e46a2..1f8e1d393f 100644
--- a/tests/test/cg/tmoddiv4.pp
+++ b/tests/test/cg/tmoddiv4.pp
@@ -1,3 +1,4 @@
+program tmoddiv4;
 
 const
   TestValues: array[0..10] of QWord = (500, 1, 0, 995, $100000000, $100000001, $7FFFFFFFFFFFFFFF, QWord($8000000000000000), QWord($8000000000000001), QWord($8000000000000002), 1000000);
@@ -107,4 +108,5 @@ begin
     Writeln(Y);
     DoCheck;
   end;
+  writeln('ok');
 end.