From 81eb67adb8d7f2fda1a50f3a58f835f65ff3a83c Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Fri, 30 Jan 2026 21:23:12 +0100
Subject: [PATCH] Add QINT

---
 STATUS.md                                    |  2 +-
 src/basic/,stubs_math/bc9b.QINT.s            | 21 --------
 src/basic/math/bc9b.QINT.s                   | 51 ++++++++++++++++++++
 src/basic/{,stubs_math => math}/bc9b.interop |  0
 tools/similarity.c                           |  3 +-
 5 files changed, 54 insertions(+), 23 deletions(-)
 delete mode 100644 src/basic/,stubs_math/bc9b.QINT.s
 create mode 100644 src/basic/math/bc9b.QINT.s
 rename src/basic/{,stubs_math => math}/bc9b.interop (100%)

diff --git a/STATUS.md b/STATUS.md
index b4fd9be6..2b26a4e4 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -239,7 +239,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BC44`   | `convert_i16_to_FAC1`  | DONE     |                                                    |
 | `$BC58`   | `abs_FAC1`             | DONE     | From the Microsoft BASIC, original name: ABS       |
 | `$BC5B`   | `FCOMP`                | DONE     |                                                    |
-| `$BC9B`   | `QINT`                 | NOT DONE | convert FAC1 to 32 bit signed integer              |
+| `$BC9B`   | `QINT`                 | DONE     | From the Microsoft BASIC, original name: QINT      |
 | `$BCCC`   | `int_FAC1`             | DONE     |                                                    |
 | `$BCE9`   | `clear_FAC1`           | DONE     | From the Microsoft BASIC, original name: CLRFAC    |
 | `$BCF3`   | `FIN`                  | PARTIAL  | Only for 38k memory model + not fully tested yet   |
diff --git a/src/basic/,stubs_math/bc9b.QINT.s b/src/basic/,stubs_math/bc9b.QINT.s
deleted file mode 100644
index 57bc0803..00000000
--- a/src/basic/,stubs_math/bc9b.QINT.s
+++ /dev/null
@@ -1,21 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - convert FAC1 to 32 bit signed integer
-;
-; Output:
-; - $62-$65, big-endian order
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 115
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-;
-
-; XXX provide implementation
-
-QINT:
-
-	+STUB_IMPLEMENTATION
diff --git a/src/basic/math/bc9b.QINT.s b/src/basic/math/bc9b.QINT.s
new file mode 100644
index 00000000..16a53917
--- /dev/null
+++ b/src/basic/math/bc9b.QINT.s
@@ -0,0 +1,51 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - Quick conversion of FAC1 to 32 bit signed integer
+;
+; Output:
+; - $62-$65, big-endian order
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 115
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+;
+
+
+QINT:
+ 	;QUICK GREATEST INTEGER FUNCTION.
+	;LEAVES INT(FAC) IN FACHO&MO&LO SIGNED.
+	;ASSUMES FAC .LT. 2^23 = 8388608
+
+	lda FAC1_exponent
+	beq clear_FAC1          ; If zero, got it.
+	sec
+	sbc #$A0                ; Get number of places to shift.
+	bit FAC1_sign
+	bpl @1
+	tax
+	lda #$FF
+	sta BITS
+	jsr neg_FAC1_mantissa
+	txa
+@1: ldx #FAC1_exponent
+    cmp #$F9
+    bpl QINT1                   ; If number of places >= 7 shift 1 place at a time.
+    jsr shiftr_FAC
+    sty BITS                    ; Zero bits since adder wants zero.
+QINT_ret:
+    rts
+
+QINT1:
+    tay                             ; Put count in counter
+    lda FAC1_sign
+    and #$80                        ; Get sign bit
+    lsr FAC1_mantissa               ; Save first shifted byte
+    ora FAC1_mantissa
+    sta FAC1_mantissa
+    jsr short_shift_FAC             ; Shift the rest
+    sty BITS                        ; Zero [BITS]
+    rts
diff --git a/src/basic/,stubs_math/bc9b.interop b/src/basic/math/bc9b.interop
similarity index 100%
rename from src/basic/,stubs_math/bc9b.interop
rename to src/basic/math/bc9b.interop
diff --git a/tools/similarity.c b/tools/similarity.c
index 1f156c7d..0eadd549 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -20,7 +20,7 @@ int matches[MAX_SIZE];
 
 int phase_mask[MAX_SIZE+MAX_SIZE];
 
-#define NUM_CHUNKS 6
+#define NUM_CHUNKS 7
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB849, 0xB84F,
@@ -28,6 +28,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB983, 0xB9BB,
     0xBBA2, 0xBC1A,
     0xBC58, 0xBC5A,
+    0xBC9B, 0xBCCB,
     0xBCE9, 0xBCF2,
 };