From 2f71ad6d2f44efda5bfaa1a1f097b8b14f9fe5e2 Mon Sep 17 00:00:00 2001
From: Virgil Dupras <hsoft@hardcoded.net>
Date: Fri, 22 Nov 2019 18:35:10 -0500
Subject: [PATCH] lib/expr: add left/right shifting operators

---
 apps/README.md                 |  8 ++++++--
 apps/lib/expr.asm              | 36 ++++++++++++++++++++++++++++++++++++
 tools/tests/unit/test_expr.asm | 10 ++++++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/apps/README.md b/apps/README.md
index 3623acc..c85b5c9 100644
--- a/apps/README.md
+++ b/apps/README.md
@@ -91,8 +91,12 @@ this way, it's going to mess with the parser.
 
 An expression is a bunch of literals or symbols assembled by operators.
 Supported operators are `+`, `-`, `*`, `/`, `%` (modulo), `&` (bitwise and),
-`|` (bitwise or) and `^` (bitwise xor). Bitwise operator always operate on
-the whole 16-bits.
+`|` (bitwise or), `^` (bitwise xor), `{` (shift left), `}` (shift right).
+Bitwise operator always operate on the whole 16-bits.
+
+Shift operators break from the `<<` and `>>` tradition because the complexity
+if two-sized operator is significant and deemed not worth it. The shift
+operator shift the left operand X times, X being the right operand.
 
 There is no parenthesis support yet.
 
diff --git a/apps/lib/expr.asm b/apps/lib/expr.asm
index 982f3fe..52e5d46 100644
--- a/apps/lib/expr.asm
+++ b/apps/lib/expr.asm
@@ -123,6 +123,10 @@ exprTbl:
 	.dw	.or
 	.db	'^'
 	.dw	.xor
+	.db	'}'
+	.dw	.rshift
+	.db	'{'
+	.dw	.lshift
 	.db	0		; end of table
 
 .plus:
@@ -198,3 +202,35 @@ exprTbl:
 	push	hl \ pop ix
 	cp	a		; ensure Z
 	ret
+
+.rshift:
+	push	ix \ pop hl
+	ld	a, l
+	and	0xf
+	ret	z
+	push	bc
+	ld	b, a
+.rshiftLoop:
+	srl	d
+	rr	e
+	djnz	.rshiftLoop
+	push	de \ pop ix
+	pop	bc
+	cp	a		; ensure Z
+	ret
+
+.lshift:
+	push	ix \ pop hl
+	ld	a, l
+	and	0xf
+	ret	z
+	push	bc
+	ld	b, a
+.lshiftLoop:
+	sla	e
+	rl	d
+	djnz	.lshiftLoop
+	push	de \ pop ix
+	pop	bc
+	cp	a		; ensure Z
+	ret
diff --git a/tools/tests/unit/test_expr.asm b/tools/tests/unit/test_expr.asm
index f8c3342..b4cdc1c 100644
--- a/tools/tests/unit/test_expr.asm
+++ b/tools/tests/unit/test_expr.asm
@@ -145,6 +145,10 @@ testParseExpr:
 	call	.testEQ
 	ld	iy, .t5
 	call	.testEQ
+	ld	iy, .t6
+	call	.testEQ
+	ld	iy, .t7
+	call	.testEQ
 	ret
 
 .testEQ:
@@ -176,6 +180,12 @@ testParseExpr:
 .t5:
 	.dw	0x96f8
 	.db	"0x99f7^0x0f0f", 0
+.t6:
+	.dw	0x133e
+	.db	"0x99f7}3", 0
+.t7:
+	.dw	0xcfb8
+	.db	"0x99f7{3", 0
 
 nexttest:
 	ld	a, (testNum)