From 33355766b4689549ac60ee211017ffc66fa3dc2a Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Tue, 14 Apr 2026 20:57:05 +0200
Subject: [PATCH] Update poly1_FAC1

---
 STATUS.md                              |  2 +-
 src/aliases/,aliases_ram_lowmem.s      |  4 +++-
 src/basic/math_trans/e043.poly1_FAC1.s | 23 ++++++++++++++---------
 tools/similarity.c                     |  3 ++-
 4 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/STATUS.md b/STATUS.md
index e9093411..22f7a032 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -257,7 +257,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BF7B`   | `pwr_FAC2_FAC1`        | NOT DONE |                                                    |
 | `$BFB4`   | `toggle_sign_FAC1`     | DONE     | From the Microsoft BASIC, original name: NEGOP     |
 | `$BFED`   | `exp_FAC1`             | NOT DONE |                                                    |
-| `$E043`   | `poly1_FAC1`           | PARTIAL  | not fully tested yet                               |
+| `$E043`   | `poly1_FAC1`           | DONE     | From the Microsoft BASIC, original name: POLYX     |
 | `$E059`   | `poly2_FAC1`           | PARTIAL  | not fully tested yet                               |
 | `$E097`   | `rnd_FAC1`             | DONE     |                                                    |
 | `$E09A`   | `rnd_A`                | DONE     |                                                    |
diff --git a/src/aliases/,aliases_ram_lowmem.s b/src/aliases/,aliases_ram_lowmem.s
index d221f916..c1a01b9e 100644
--- a/src/aliases/,aliases_ram_lowmem.s
+++ b/src/aliases/,aliases_ram_lowmem.s
@@ -69,6 +69,7 @@
 	!addr FAC1_sign       = $66
 
 	!addr SGNFLG    = $67 ;          Also used as number of terms of series evaluation
+	!addr DEGREE    = SGNFLG
 	!addr BITS      = $68 ;          FAC1 overflow
 
 	!addr __FAC2    = $69 ; $69-$6E  floating point accumulator 2 [!] also used for memory move pointers
@@ -78,7 +79,8 @@
 
 	!addr ARISGN    = $6F ;          -- NOT IMPLEMENTED --
 	!addr FACOV     = $70 ;          FAC1 low order mantissa
-	!addr FBUFPT    = $71 ; $71-$72  -- NOT IMPLEMENTED --
+	!addr FBUFPT    = $71 ; $71-$72
+	!addr POLYPT    = FBUFPT
 	!addr CHRGET    = $73 ; $73-$8A  copied from $E3A2 during cold start
 	!addr CHRGOT    = $79 ; same area as CHRGET
 	!addr TXTPTR    = $7A ; $7A-$7B  current BASIC statement pointer
diff --git a/src/basic/math_trans/e043.poly1_FAC1.s b/src/basic/math_trans/e043.poly1_FAC1.s
index 970c277e..f02422f3 100644
--- a/src/basic/math_trans/e043.poly1_FAC1.s
+++ b/src/basic/math_trans/e043.poly1_FAC1.s
@@ -2,9 +2,13 @@
 ;; #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 - evaluate polynomial with odd powers only for FAC1 value
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named POLYX.
+;
 ; Input:
 ; - .A - table address low byte
 ; - .Y - table address low byte
@@ -25,14 +29,15 @@
 
 
 poly1_FAC1:
-    jsr store_YA_in_ZP              ; Store YA in second INDEX pointer
-    jsr mov_r_FAC1_TMP1             ; TMPF1 <- FAC1  (rounds)
-    jsr mov_FAC1_FAC2               ; FAC2 <- FAC1
-    jsr mul_FAC2_FAC1               ; FAC1 <- FAC1 * FAC2  (x^2)
-    jsr poly2_table_in_index2       ; poly2: skip storing YA to ZP
-    ldy #$00                        ; FAC1 <- FAC1 * TEMPF1
-    lda #TEMPF1
-    jmp mul_MEM_FAC1
+        sta POLYPT            ; Retain polynomial pointer for later
+        sty POLYPT+1
+        jsr mov_r_FAC1_TMP1     ; Save FAC1 in TMP1
+        lda #TEMPF1
+        jsr mul_MEM_FAC1        ; Compute x^2
+        jsr POLY1               ; Compute P(x^2)
+        lda #<TEMPF1
+        ldy #>TEMPF1
+        jmp mul_MEM_FAC1        ; Multiply by FAC1 again
 
 
 } else {
diff --git a/tools/similarity.c b/tools/similarity.c
index d0f9acf9..81f586c5 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 11
+#define NUM_CHUNKS 12
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB391, 0xB39D,
@@ -32,6 +32,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xBDB3, 0xBDC1,
     0xBDDD, 0xBF51,
     0xBFB4, 0xBFEC,
+    0xE043, 0xE058,
     0xE264, 0xE2C2,     // Two byte gap here is an optimization
     0xE2C5, 0xE37A,
 };