Fix how 'ADC A,*' and 'SBC A,*' affect the half-carry flag

skoolkid · Aug 13, 2024 · 058268d · 058268d
1 parent c734fd5
commit 058268d
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Showing 4 changed files with 8 additions and 7 deletions.
diff --git a/c/csimulator.c b/c/csimulator.c
@@ -244,7 +244,7 @@ static void init_ADC() {
                     ADC[c][a][i][1] = (
                         (v & 0xA8)                                           // S.5.3.N.
                         + (((v & 0xFF) == 0) ? 0x40 : 0)                     // .Z......
-                        + (((a & 0x0F) + ((v - a) & 0x0F)) & 0x10)           // ...H....
+                        + ((v ^ a ^ (v - c - a)) & 0x10)                     // ...H....
                         + (((a ^ (v - c - a) ^ 0x80) & (a ^ v) & 0x80) >> 5) // .....P..
                         + ((v > 0xFF) ? 0x01 : 0)                            // .......C
                     );
@@ -561,7 +561,7 @@ static void init_SBC() {
                     SBC[c][a][i][1] = (
                         (v & 0xA8)                                    // S.5.3...
                         + (((v & 0xFF) == 0) ? 0x40 : 0)              // .Z......
-                        + (((a & 0x0F) - ((a - v) & 0x0F)) & 0x10)    // ...H....
+                        + ((v ^ a ^ (a - v - c)) & 0x10)              // ...H....
                         + (((a ^ (a - v - c)) & (a ^ v) & 0x80) >> 5) // .....P..
                         + 0x02                                        // ......N.
                         + ((v < 0) ? 1 : 0)                           // .......C

diff --git a/skoolkit/simtables.py b/skoolkit/simtables.py
@@ -1,4 +1,4 @@
-# Copyright 2022 Richard Dymond (rjdymond@gmail.com)
+# Copyright 2022, 2024 Richard Dymond (rjdymond@gmail.com)
 #
 # This file is part of SkoolKit.
 #
@@ -27,7 +27,7 @@
         v % 256,
         (v & 0xA8)                                           # S.5.3.N.
         + (v % 256 == 0) * 0x40                              # .Z......
-        + (((a % 16) + ((v - a) % 16)) & 0x10)               # ...H....
+        + ((v ^ a ^ (v - c - a)) & 0x10)                     # ...H....
         + ((a ^ (v - c - a) ^ 0x80) & (a ^ v) & 0x80) // 32  # .....P..
         + (v > 0xFF)                                         # .......C
     ) for v in range(a + c, a + c + 256)
@@ -236,7 +236,7 @@
         v % 256,
         (v & 0xA8)                                    # S.5.3...
         + (v % 256 == 0) * 0x40                       # .Z......
-        + (((a % 16) - ((a - v) % 16)) & 0x10)        # ...H....
+        + ((v ^ a ^ (a - v - c)) & 0x10)              # ...H....
         + ((a ^ (a - v - c)) & (a ^ v) & 0x80) // 32  # .....P..
         + 0x02                                        # ......N.
         + (v < 0)                                     # .......C

diff --git a/sphinx/source/changelog.rst b/sphinx/source/changelog.rst
@@ -3,6 +3,7 @@ Changelog
 
 9.4b1
 -----
+* Fixed how the 'ADC A,*' and 'SBC A,*' instructions affect the half-carry flag
 
 9.3 (2024-08-10)
 ----------------

diff --git a/tests/slow_test_simulator.py b/tests/slow_test_simulator.py
@@ -460,7 +460,7 @@ def test_add_a_a(self):
         self._verify(AFTracer(135), '8a5b656618120683ff1e8b2c91e55315')
 
     def test_adc_a_r(self):
-        self._verify(AFRTracer(136), '0ae2d98f422d958f8ca77645a3b17aad')
+        self._verify(AFRTracer(136), '88c87db326d118846416ca8c4a18ee8f')
 
     def test_adc_a_a(self):
         self._verify(AFTracer(143), 'af1966e41681c026ad6c9d6e12fc3ed8')
@@ -472,7 +472,7 @@ def test_sub_a(self):
         self._verify(AFTracer(151), 'f83836b3beef2cf62227b74fa2db50d5')
 
     def test_sbc_a_r(self):
-        self._verify(AFRTracer(152), 'b4cbffcca3bdc458fd705d0b3dbcd3d9')
+        self._verify(AFRTracer(152), '9fc1dc7e21f660f87fbcc7649e0303b6')
 
     def test_sbc_a_a(self):
         self._verify(AFTracer(159), '56af67d5c20e1fe7956207a4059edcc6')