From eedcd970e503c0bf72ec1a1af5e6995752f47e0e Mon Sep 17 00:00:00 2001
From: julianb0 <spectral@os-k.eu>
Date: Thu, 13 Jun 2019 15:47:20 +0200
Subject: [PATCH] more doc

---
 vm/in/INSTRS   | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
 vm/in/arith.c  | 22 +++-------------------
 vm/in/flags.h  |  9 +++++++++
 vm/in/string.c | 18 ++++++++++++++++++
 4 files changed, 76 insertions(+), 21 deletions(-)

diff --git a/vm/in/INSTRS b/vm/in/INSTRS
index 66d5bea..046c98a 100644
--- a/vm/in/INSTRS
+++ b/vm/in/INSTRS
@@ -206,7 +206,7 @@ div2 rim
 #---------------------------------------------------------------------------#
 
 #
-# TEST Comparaison instruction
+# TEST Comparison instruction
 #
 #       $1 AND $2
 #
@@ -216,7 +216,7 @@ div2 rim
 test rim rim
 
 #
-# CMP Comparaison instruction
+# CMP Comparison instruction
 #
 #       $1 - $2
 #
@@ -416,6 +416,50 @@ lodsb
 lodsb r
 lodsb rm r
 
+#
+# Scan string for a particular value (SCASx)
+#
+#       CMP([%str], $val)
+#
+#       IF (DF == 0) THEN
+#           %str = %str + sizeof(x)
+#       ELSE
+#           %str = %str - sizeof(x)
+#       FI
+#
+# Sets CF, OF, ZF and SF according to the result of the comparison
+#
+# When no parameters are given, %str = RDI and $val = RAX
+# When one parameter is given, %str = RDI and $val = $1
+# When two parameters are given, %str = $1 and $val = $2
+#
+scasb
+scasb rim
+scasb r rim
+
+#
+# Compare bytes in strings (CMPSx)
+#
+#       CMP([%str1], [%str2])
+#
+#       IF (DF == 0) THEN
+#           %str1 = %str1 + sizeof(x)
+#           %str2 = %str2 + sizeof(x)
+#       ELSE
+#           %str1 = %str1 - sizeof(x)
+#           %str2 = %str2 - sizeof(x)
+#       FI
+#
+# Sets CF, OF, ZF and SF according to the result of the comparison
+#
+# When no parameters are given, %str1 = RDI and %str2 = RSI
+# When one parameter is given, %str1 = RDI and %str2 = $1
+# When two parameters are given, %str1 = $1 and %str2 = $2
+#
+cmpsb
+cmpsb r
+cmpsb r r
+
 #
 # Move value from string to string (MOVSx)
 #
diff --git a/vm/in/arith.c b/vm/in/arith.c
index f190ea5..99e05c5 100644
--- a/vm/in/arith.c
+++ b/vm/in/arith.c
@@ -100,32 +100,17 @@ IMPL_OUT;
 
 IMPL_START_2(subf)
 {
-    if (v1 < v2) flg |= CF;
-    else flg &= ~CF;
-
-    if ( ((v2 < 0) && (v1 > LONG_MAX + v2))
-      || ((v2 > 0) && (v1 < LONG_MIN + v2)) )
-         flg |= OF;
-    else flg &= ~OF;
-
+    COMPARE(v1, v2);
     v1 -= v2;
 }
-IMPL_OUT_ZSF;
+IMPL_OUT;
 
 //
 // i_subf but discards result
 //
 IMPL_START_2(cmp)
 {
-    if (v1 < v2) flg |= CF;
-    else flg &= ~CF;
-
-    if ( ((v2 < 0) && (v1 > LONG_MAX + v2))
-      || ((v2 > 0) && (v1 < LONG_MIN + v2)) )
-        flg |= OF;
-    else flg &= ~OF;
-
-    SET_ZSF(v1 - v2);
+    COMPARE(v1, v2);
 }
 IMPL_END;
 
@@ -180,7 +165,6 @@ IMPL_START_2(mulf)
 }
 IMPL_OUT;
 
-
 IMPL_START_1(mul2)
 {
     multiply(rax, v1, &rdx, &rax);
diff --git a/vm/in/flags.h b/vm/in/flags.h
index ecbe3e2..c99843c 100644
--- a/vm/in/flags.h
+++ b/vm/in/flags.h
@@ -21,3 +21,12 @@
     SET_SF(v);                                                              \
     SET_PF(v)
 
+#define COMPARE(v1, v2)                                                     \
+    if (v1 < v2) flg |= CF;                                                 \
+    else flg &= ~CF;                                                        \
+    if ( ((v2 < 0) && (v1 > LONG_MAX + v2))                                 \
+      || ((v2 > 0) && (v1 < LONG_MIN + v2)) )                               \
+        flg |= OF;                                                          \
+    else flg &= ~OF;                                                        \
+    SET_ZSF(v1 - v2);
+
diff --git a/vm/in/string.c b/vm/in/string.c
index f355502..91ca0fa 100644
--- a/vm/in/string.c
+++ b/vm/in/string.c
@@ -10,11 +10,29 @@ IMPL_START_0(stosb)
 }
 IMPL_END;
 
+//----------------------------------------------------------------------------//
+
 IMPL_START_0(lodsb)
 {
 }
 IMPL_END;
 
+//----------------------------------------------------------------------------//
+
+IMPL_START_0(scasb)
+{
+}
+IMPL_END;
+
+//----------------------------------------------------------------------------//
+
+IMPL_START_0(cmpsb)
+{
+}
+IMPL_END;
+
+//----------------------------------------------------------------------------//
+
 IMPL_START_0(movsb)
 {
 }