From 360e1525ae80c98ac7c1c76cbd24d254e0774352 Mon Sep 17 00:00:00 2001
From: David Given <dtrg@google.com>
Date: Tue, 12 Feb 2019 11:57:37 +0100
Subject: [PATCH] Replace the non-working Z80 style signed comparison sign
 adjustment with something which actually works on the 8080. Sadly, Star Trek
 is up to 40243 bytes again.

---
 mach/i80/libem/rst.s | 12 +---------
 mach/i80/ncg/table   | 56 +++++++++++++++++++++++++++-----------------
 2 files changed, 35 insertions(+), 33 deletions(-)

diff --git a/mach/i80/libem/rst.s b/mach/i80/libem/rst.s
index 2e13584e5..a5234bd67 100644
--- a/mach/i80/libem/rst.s
+++ b/mach/i80/libem/rst.s
@@ -17,11 +17,6 @@
     shld 0x11
     lxi h, rst3
     shld 0x19
-
-    lhld rst4
-    shld 0x20
-    lhld rst4+2
-    shld 0x22
     ret
 
     ! de = [bc+const1] (remember bc is the frame pointer)
@@ -74,9 +69,4 @@ rst3:
 
     dad b
     ret
-    
-    ! Adjust flags for signed comparison
-rst4:
-    rpo
-    xri 0x80
-    ret
+
diff --git a/mach/i80/ncg/table b/mach/i80/ncg/table
index 963a1f07f..1af10558a 100644
--- a/mach/i80/ncg/table
+++ b/mach/i80/ncg/table
@@ -13,12 +13,6 @@ EM_WSIZE = 2
 EM_PSIZE = 2
 EM_BSIZE = 4
 
-#ifdef USE_I80_RSTS
-   #define SIGN_ADJUST rst {const1, 4}
-#else
-   #define SIGN_ADJUST jpo {label, 1f} xri {const1, 0x80} 1:
-#endif
-
 SL=4
 
 PROPERTIES
@@ -1862,30 +1856,39 @@ pat blt
    with const2 hl_or_de STACK
       uses areg
       gen
+         mov a, %2.1
+         xri {const1, 0x80}
+         mov %2.1, a
          mov a, %2.2
          sui {const1, %1.num & 0xff}
          mov a, %2.1
-         sbi {const1, %1.num >> 8}
-         SIGN_ADJUST
-         jm {label, $1}
+         sbi {const1, (%1.num >> 8) ^ 0x80}
+         jc {label, $1}
    with hl_or_de const2 STACK
       uses areg
       gen
+         mov a, %1.1
+         xri {const1, 0x80}
+         mov %1.1, a
          mvi a, {const1, %2.num & 0xff}
          sub %1.2
-         mvi a, {const1, %2.num >> 8}
+         mvi a, {const1, (%2.num >> 8) ^ 0x80}
          sbb %1.1
-         SIGN_ADJUST
-         jm {label, $1}
+         jc {label, $1}
    with hl_or_de hl_or_de STACK
       uses areg
       gen
+         mov a, %2.1
+         xri {const1, 0x80}
+         mov %2.1, a
+         mov a, %1.1
+         xri {const1, 0x80}
+         mov %1.1, a
          mov a, %2.2
          sub %1.2
          mov a, %2.1
          sbb %1.1
-         SIGN_ADJUST
-         jm {label,$1}
+         jc {label,$1}
 
 pat bgt
    leaving
@@ -1896,30 +1899,39 @@ pat bge
    with const2 hl_or_de STACK
       uses areg
       gen
+         mov a, %2.1
+         xri {const1, 0x80}
+         mov %2.1, a
          mov a, %2.2
          sui {const1, %1.num & 0xff}
          mov a, %2.1
-         sbi {const1, %1.num >> 8}
-         SIGN_ADJUST
-         jp {label, $1}
+         sbi {const1, (%1.num >> 8) ^ 0x80}
+         jnc {label, $1}
    with hl_or_de const2 STACK
       uses areg
       gen
+         mov a, %1.1
+         xri {const1, 0x80}
+         mov %1.1, a
          mvi a, {const1, %2.num & 0xff}
          sub %1.2
-         mvi a, {const1, %2.num >> 8}
+         mvi a, {const1, (%2.num >> 8) ^ 0x80}
          sbb %1.1
-         SIGN_ADJUST
-         jp {label, $1}
+         jnc {label, $1}
    with hl_or_de hl_or_de STACK
       uses areg
       gen
+         mov a, %2.1
+         xri {const1, 0x80}
+         mov %2.1, a
+         mov a, %1.1
+         xri {const1, 0x80}
+         mov %1.1, a
          mov a,%2.2
          sub %1.2
          mov a,%2.1
          sbb %1.1
-         SIGN_ADJUST
-         jp {label,$1}
+         jnc {label,$1}
 
 pat ble
    leaving