Add pwr_FAC2_FAC1

src/aliases/,aliases_ram_lowmem.s

@@ -15,6 +15,7 @@
 	!addr ADRAY1    = $03 ; $03-$04
 	!addr ADRAY2    = $05 ; $05-$06
 	!addr CHARAC    = $07 ;          [!] our implementation might be different  XXX give more details
+	!addr INTEGR    = CHARAC
 	!addr ENDCHR    = $08 ;          [!] our implementation might be different  XXX give more details
 	!addr TRMPOS    = $09 ;          -- NOT IMPLEMENTED -- [!] on MEGA65 also used by DOS Wedge under MONITOR
 	!addr VERCKB    = $0A ;          flag used by BASIC, 0 - LOAD, 1 - VERIFY, [!] on MEGA65 also used by DOS Wedge

src/basic/,stubs_math/bf7b.pwr_FAC2_FAC1.s

@@ -1,26 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - set FAC1 as FAC2 raised to the power of FAC1
-;
-; Input:
-; - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
-;
-; Note:
-; - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
-; - uses exp(x*log(y)) formula to calculate y^x; slow and inaccurate
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 117
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-;
-
-; XXX provide implementation
-
-pwr_FAC2_FAC1:
-
-	+STUB_IMPLEMENTATION

src/basic/math_trans/bf7b.pwr_FAC2_FAC1.s

@@ -0,0 +1,74 @@
+;; #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 - set FAC1 as FAC2 raised to the power of FAC1
+;
+; This is verified to be almost identical to the original Microsoft implementation where it was named FPWRT.
+;
+; Input:
+; - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
+;
+; Note:
+; - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
+; - uses exp(x*log(y)) formula to calculate y^x; slow and inaccurate
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 117
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+; EXPONENTIATION ---  X^Y.
+; N.B.  0^0=1
+; FIRST CHECK IF Y=0. IF SO, THE RESULT IS 1.
+; NEXT CHECK IF X=0. IF SO THE RESULT IS 0.
+; THEN CHECK IF X.GT.0. IF NOT CHECK THAT Y IS AN INTEGER.
+; IF SO, NEGATE X, SO THAT LOG DOESN'T GIVE FCERR.
+; IF X IS NEGATIVE AND Y IS ODD, NEGATE THE RESULT
+; RETURNED BY EXP.
+; TO COMPUTE THE RESULT USE X^Y=EXP((Y*LOG(X)).
+
+!ifdef CONFIG_TRANSCENDENTAL_FUNCTIONS {
+!ifdef CONFIG_MEMORY_MODEL_38K {
+
+pwr_FAC2_FAC1:
+
+    beq exp_FAC1        ; If FAC1=0, just exponentiate that
+    lda FAC2_exponent   ; Is X=0?
+    bne FPWRT1
+    jmp ZEROF1          ; Zero FAC1
+FPWRT1:
+    ldx #TEMPF3         ; Save for later in a temp
+    ldy #0
+    jsr mov_r_FAC1_MEM
+	; Y=0 already. Good in case no one calls INT
+    lda FAC2_sign
+    bpl FPWR1           ; No problems if X>0
+    jsr int_FAC1        ; Integerize the FAC1
+    lda #TEMPF3         ; Get addr of comperand
+    ldy #0
+    jsr FCOMP           ; Equal?
+    bne FPWR1           ; Leave X neg. log will blow him out. A=-1 and Y is irrelevant
+    tya                 ; Negate X. Make positive
+    ldy INTEGR          ; Get evenness
+FPWR1:
+    jsr mov_FAC2_FAC1_sign      ; Alternate entry point
+    tya
+    pha                 ; Save evenness for later
+    jsr log_FAC1        ; Find log
+    lda #TEMPF3         ; Multiply FAC1 times log(x)
+    ldy #0
+    jsr mul_MEM_FAC1
+    jsr exp_FAC1        ; Exponentiate the FAC1
+    pla
+    lsr                 ; Is it even=
+    bcc NEGRTS          ; Yes. or X>0
+
+    ; FALLTHROUGH to toggle_sign_FAC1
+}
+}