From 74d1943cee4f278cd4fbc2acd593c108cc5f0d6b Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Sat, 31 Jan 2026 14:48:09 +0100
Subject: [PATCH] Update int_FAC1

---
 src/basic/math/bccc.int_FAC1.jmp.s |  8 ----
 src/basic/math/bccc.int_FAC1.s     | 34 ++++++++++++++++
 src/basic/math/int_FAC1.s          | 65 ------------------------------
 3 files changed, 34 insertions(+), 73 deletions(-)
 delete mode 100644 src/basic/math/bccc.int_FAC1.jmp.s
 create mode 100644 src/basic/math/bccc.int_FAC1.s
 delete mode 100644 src/basic/math/int_FAC1.s

diff --git a/src/basic/math/bccc.int_FAC1.jmp.s b/src/basic/math/bccc.int_FAC1.jmp.s
deleted file mode 100644
index c6e6e130..00000000
--- a/src/basic/math/bccc.int_FAC1.jmp.s
+++ /dev/null
@@ -1,8 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-; Just a compatibility jump - our routine is longer than original one
-
-	jmp int_FAC1
diff --git a/src/basic/math/bccc.int_FAC1.s b/src/basic/math/bccc.int_FAC1.s
new file mode 100644
index 00000000..0e0ba3f1
--- /dev/null
+++ b/src/basic/math/bccc.int_FAC1.s
@@ -0,0 +1,34 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
+
+; Math package - rounds away the decimal to make an integer
+;
+; This is verified to be identical to the original Microsoft implementation where it was named INT.
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 116
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+int_FAC1:
+
+    lda FAC1_exponent
+    cmp #$A0
+    bcs clear_FAC1_rts
+    jsr QINT
+    sty FACOV
+    lda FAC1_sign
+    sty FAC1_sign
+    eor #$80
+    rol
+    lda #$A0
+    sta FAC1_exponent
+    lda FAC1_mantissa+3
+    sta CHARAC                  ; INTEGR in the original code ($07)
+    jmp abs_and_normal_FAC1
diff --git a/src/basic/math/int_FAC1.s b/src/basic/math/int_FAC1.s
deleted file mode 100644
index 8e37b9ed..00000000
--- a/src/basic/math/int_FAC1.s
+++ /dev/null
@@ -1,65 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - rounds away the decimal to make an integer
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 116
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-;
-
-int_FAC1:
-
-    lda FAC1_exponent
-    cmp #$81
-    bcc int_FAC1_zero           ; exponent is 0 or lower so integer part is 0
-    cmp #$A0
-    bcs int_FAC1_out            ; exponent is 32 or larger so the entire mantissa is part of the integer
-
-    tax
-    and #$07                    ; low three bits of exponent is number of bits to keep
-    tay
-    
-    txa
-    lsr                         ; Bits 4-5 of exponent is how many full mantissa bytes to keep
-    lsr
-    lsr
-    and #$03
-    tax
-
-    lda #$FF                    ; Create bit mask for first mantissa byte to change
-@1: lsr
-    dey
-    bne @1
-    eor #$FF
-
-    and FAC1_mantissa,X
-    sta FAC1_mantissa,X
-    lda #0
-@2: inx
-    cpx #$4
-    bcs @3
-    sta FAC1_mantissa,X
-    bcc @2
-
-@3: lda FAC1_sign
-    bpl int_FAC1_out
-    lda #<const_ONE             ; If negative subtract one
-    ldy #>const_ONE
-    jsr sub_MEM_FAC1            ; FAC1 = 1 - FAC1
-    lda #$FF
-    sta FAC1_sign               ; FAC1 = FAC1 - 1
-    rts
-
-
-    ; FIXME: Do we need to set FACOV to 0?
-
-int_FAC1_zero:
-    lda #0
-    sta FAC1_exponent
-int_FAC1_out:
-    rts