From 61bb22e8c924f9ae8f039024d51a3c0fde76da68 Mon Sep 17 00:00:00 2001
From: Virgil Dupras <hsoft@hardcoded.net>
Date: Wed, 25 Mar 2020 21:49:09 -0400
Subject: [PATCH] forth: straighten out "/MOD"

The removal of the "divide" routine highlighted the fact that
nativeWord wasn't properly stabilized.
---
 emul/forth/z80c.bin | Bin 288 -> 288 bytes
 forth/forth.asm     |  60 ++++++++++++++++++--------------------------
 forth/z80c.fs       |   2 +-
 3 files changed, 25 insertions(+), 37 deletions(-)

diff --git a/emul/forth/z80c.bin b/emul/forth/z80c.bin
index ffa729c26ab2f3a30ec277de063492952cb343e8..74adf553b3c011b243779439a72cb84a691871cf 100644
GIT binary patch
literal 288
zcmWIY4`BcTb_ND<hKCmqo|R>|`t;~wDF!2#&;X#gC`24AeDx_v+&|1U2rho`??a%}
z-={~fJ_QmW>ELijpgtL>abRhfoTHx$$SO&=k=0A{tCpmLO!WsE2?P=dsjc}{TfkBg
z5IH2NwfR+Rz*5eNXu67lMmalx1%<#y0Uej8#sIP*0HRm~BzzF$=(m|*QLt)ZuqaSa
Pjp1zuNOe2}0DTVt6s=p*

literal 288
zcmWIY4`BcTb_RxRj1Mm!JS)p^_36>WQVd2ep#eZ~QHVHL`07)TxPO>y5M2D=--ke{
zzfX@|eF`K%(!t@5Kz%Y$<G|7|IY&PikX4d!BdeF@S1m~gnd%QT5(p#^Qd{$@wt%G~
zAaY1jYxAqtfTf%j(R399jdFGX3krda0y-{FjR9ms07S6}NcbSg(Qh-sqF~j+U{Ro;
P8pGQRkm`5{0Qw#P3Z7!J

diff --git a/forth/forth.asm b/forth/forth.asm
index 4cf14ea..3f7c6d8 100644
--- a/forth/forth.asm
+++ b/forth/forth.asm
@@ -106,8 +106,9 @@
 ; *** Stable ABI ***
 ; Those jumps below are supposed to stay at these offsets, always. If they
 ; change bootstrap binaries have to be adjusted because they rely on them.
-.fill 0x1a-$
+.fill 0x17-$
 JUMPTBL:
+	jp	nativeWord
 	jp	next
 	jp	chkPS
 
@@ -298,35 +299,6 @@ strskip:
 	pop	bc
 	ret
 
-; Borrowed from Tasty Basic by Dimitri Theulings (GPL).
-; Divide HL by DE, placing the result in BC and the remainder in HL.
-divide:
-	push hl		; --> lvl 1
-	ld l, h		; divide h by de
-	ld h, 0
-	call .dv1
-	ld b, c		; save result in b
-	ld a, l		; (remainder + l) / de
-	pop hl		; <-- lvl 1
-	ld h, a
-.dv1:
-	ld c, 0xff	; result in c
-.dv2:
-	inc c		; dumb routine
-	call .subde	; divide using subtract and count
-	jr nc, .dv2
-	add hl, de
-	ret
-.subde:
-	ld a, l
-	sub e		; subtract de from hl
-	ld l, a
-	ld a, h
-	sbc a, d
-	ld h, a
-	ret
-
-
 ; Parse string at (HL) as a decimal value and return value in DE.
 ; Reads as many digits as it can and stop when:
 ; 1 - A non-digit character is read
@@ -782,10 +754,10 @@ ROUTINE:
 	ld	de, compiledWord
 	cp	'L'
 	jr	z, .end
-	ld	de, nativeWord
+	ld	de, JUMPTBL
 	cp	'V'
 	jr	z, .end
-	ld	de, JUMPTBL
+	ld	de, JUMPTBL+3
 	cp	'N'
 	jr	z, .end
 	ld	de, sysvarWord
@@ -800,7 +772,7 @@ ROUTINE:
 	ld	de, NUMBER
 	cp	'M'
 	jr	z, .end
-	ld	de, JUMPTBL+3
+	ld	de, JUMPTBL+6
 	cp	'P'
 	jr	nz, .notgood
 	; continue to end on match
@@ -1433,6 +1405,8 @@ MULT:
 	jp	next
 
 
+; Borrowed from http://wikiti.brandonw.net/
+; Divides AC by DE and places the quotient in AC and the remainder in HL
 	.db	"/MOD"
 	.fill	3
 	.dw $-MULT
@@ -1440,10 +1414,24 @@ MULT:
 DIVMOD:
 	.dw nativeWord
 	pop	de
-	pop	hl
+	pop	bc
 	call	chkPS
-	call	divide
-	push	hl
+	ld	a, b		; AC
+	ld	b, 16
+	ld	hl, 0
+.loop:
+	scf
+	rl	c
+	rla
+	adc	hl, hl
+	sbc	hl, de
+	jr	nc, .skip
+	add	hl, de
+	dec	c
+.skip:
+	djnz	.loop
+	ld	b, a
+	push	hl	; REM
 	push	bc
 	jp	next
 
diff --git a/forth/z80c.fs b/forth/z80c.fs
index e2f0e19..db5205b 100644
--- a/forth/z80c.fs
+++ b/forth/z80c.fs
@@ -24,7 +24,7 @@ CODE ROT
     HL POPqq,       ( C )
     DE POPqq,       ( B )
     BC POPqq,       ( A )
-    ROUTINE P CALLnn,
+    chkPS,
     DE PUSHqq,      ( B )
     HL PUSHqq,      ( C )
     BC PUSHqq,      ( A )