[dev.cc] cmd/asm: fix the expression parser and add tests
Rewrite the grammar to have one more production so it parses
~0*0
correctly and write tests to prove it.
Change-Id: I0dd652baf65b48a3f26c9287c420702db4eaec59
Reviewed-on: https://go-review.googlesource.com/3443
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/cmd/asm/internal/asm/expr_test.go b/src/cmd/asm/internal/asm/expr_test.go
new file mode 100644
index 0000000..2ca6625
--- /dev/null
+++ b/src/cmd/asm/internal/asm/expr_test.go
@@ -0,0 +1,71 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package asm
+
+import (
+ "cmd/asm/internal/lex"
+ "testing"
+ "text/scanner"
+)
+
+type exprTest struct {
+ input string
+ output int64
+ atEOF bool
+}
+
+var exprTests = []exprTest{
+ // Simple
+ {"0", 0, true},
+ {"3", 3, true},
+ {"070", 8 * 7, true},
+ {"0x0f", 15, true},
+ {"0xFF", 255, true},
+ {"9223372036854775807", 9223372036854775807, true}, // max int64
+ // Unary
+ {"-0", 0, true},
+ {"~0", -1, true},
+ {"~0*0", 0, true},
+ {"+3", 3, true},
+ {"-3", -3, true},
+ {"-9223372036854775808", -9223372036854775808, true}, // min int64
+ // Binary
+ {"3+4", 3 + 4, true},
+ {"3-4", 3 - 4, true},
+ {"2|5", 2 | 5, true},
+ {"3^4", 3 ^ 4, true},
+ {"3*4", 3 * 4, true},
+ {"14/4", 14 / 4, true},
+ {"3<<4", 3 << 4, true},
+ {"48>>3", 48 >> 3, true},
+ {"3&9", 3 & 9, true},
+ // General
+ {"3*2+3", 3*2 + 3, true},
+ {"3+2*3", 3 + 2*3, true},
+ {"3*(2+3)", 3 * (2 + 3), true},
+ {"3*-(2+3)", 3 * -(2 + 3), true},
+ {"3<<2+4", 3<<2 + 4, true},
+ {"3<<2+4", 3<<2 + 4, true},
+ {"3<<(2+4)", 3 << (2 + 4), true},
+ // Junk at EOF.
+ {"3 x", 3, false},
+}
+
+func TestExpr(t *testing.T) {
+ p := NewParser(nil, nil, nil) // Expression evaluation uses none of these fields of the parser.
+ for i, test := range exprTests {
+ p.start(lex.Tokenize(test.input))
+ result := int64(p.expr())
+ if result != test.output {
+ t.Errorf("%d: %q evaluated to %d; expected %d", i, test.input, result, test.output)
+ }
+ tok := p.next()
+ if test.atEOF && tok.ScanToken != scanner.EOF {
+ t.Errorf("%d: %q: at EOF got %s", i, test.input, tok)
+ } else if !test.atEOF && tok.ScanToken == scanner.EOF {
+ t.Errorf("%d: %q: expected not EOF but at EOF", i, test.input)
+ }
+ }
+}
diff --git a/src/cmd/asm/internal/asm/parse.go b/src/cmd/asm/internal/asm/parse.go
index e1e3af2..18ec932 100644
--- a/src/cmd/asm/internal/asm/parse.go
+++ b/src/cmd/asm/internal/asm/parse.go
@@ -345,7 +345,15 @@
return true
}
-// expr = term | term '+' term
+// Note: There are two changes in the expression handling here
+// compared to the old yacc/C implemenatations. Neither has
+// much practical consequence because the expressions we
+// see in assembly code are simple, but for the record:
+//
+// 1) Evaluation uses uint64; the old one used int64.
+// 2) Precedence uses Go rules not C rules.
+
+// expr = term | term ('+' | '-' | '|' | '^') term.
func (p *Parser) expr() uint64 {
value := p.term()
for {
@@ -393,56 +401,63 @@
return 0
}
-// term = const | term '*' term | '(' expr ')'
+// term = factor | factor ('*' | '/' | '%' | '>>' | '<<' | '&') factor
func (p *Parser) term() uint64 {
+ value := p.factor()
+ for {
+ switch p.peek() {
+ case '*':
+ p.next()
+ value *= p.factor() // OVERFLOW?
+ case '/':
+ p.next()
+ value /= p.factor()
+ case '%':
+ p.next()
+ value %= p.factor()
+ case lex.LSH:
+ p.next()
+ shift := p.factor()
+ if shift < 0 {
+ p.errorf("negative left shift %d", shift)
+ }
+ value <<= uint(shift) // OVERFLOW?
+ case lex.RSH:
+ p.next()
+ shift := p.term()
+ if shift < 0 {
+ p.errorf("negative right shift %d", shift)
+ }
+ value >>= uint(shift)
+ case '&':
+ p.next()
+ value &= p.factor()
+ default:
+ return value
+ }
+ }
+ p.errorf("unexpected %s evaluating expression", p.peek())
+ return 0
+}
+
+// factor = const | '+' factor | '-' factor | '~' factor | '(' expr ')'
+func (p *Parser) factor() uint64 {
tok := p.next()
switch tok.ScanToken {
+ case scanner.Int:
+ return p.atoi(tok.String())
+ case '+':
+ return +p.factor()
+ case '-':
+ return -p.factor()
+ case '~':
+ return ^p.factor()
case '(':
v := p.expr()
if p.next().ScanToken != ')' {
p.errorf("missing closing paren")
}
return v
- case '+':
- return +p.term()
- case '-':
- return -p.term()
- case '~':
- return ^p.term()
- case scanner.Int:
- value := p.atoi(tok.String())
- for {
- switch p.peek() {
- case '*':
- p.next()
- value *= p.term() // OVERFLOW?
- case '/':
- p.next()
- value /= p.term()
- case '%':
- p.next()
- value %= p.term()
- case lex.LSH:
- p.next()
- shift := p.term()
- if shift < 0 {
- p.errorf("negative left shift %d", shift)
- }
- value <<= uint(shift)
- case lex.RSH:
- p.next()
- shift := p.term()
- if shift < 0 {
- p.errorf("negative right shift %d", shift)
- }
- value >>= uint(shift)
- case '&':
- p.next()
- value &= p.term()
- default:
- return value
- }
- }
}
p.errorf("unexpected %s evaluating expression", tok)
return 0
diff --git a/src/cmd/asm/internal/lex/input.go b/src/cmd/asm/internal/lex/input.go
index eefd6eb..a193649 100644
--- a/src/cmd/asm/internal/lex/input.go
+++ b/src/cmd/asm/internal/lex/input.go
@@ -46,7 +46,7 @@
if i > 0 {
name, value = name[:i], name[i+1:]
}
- tokens := tokenize(name)
+ tokens := Tokenize(name)
if len(tokens) != 1 || tokens[0].ScanToken != scanner.Ident {
fmt.Fprintf(os.Stderr, "asm: parsing -D: %q is not a valid identifier name\n", tokens[0])
flags.Usage()
@@ -54,7 +54,7 @@
macros[name] = &Macro{
name: name,
args: nil,
- tokens: tokenize(value),
+ tokens: Tokenize(value),
}
}
return macros
diff --git a/src/cmd/asm/internal/lex/lex.go b/src/cmd/asm/internal/lex/lex.go
index 4785350..45224fe 100644
--- a/src/cmd/asm/internal/lex/lex.go
+++ b/src/cmd/asm/internal/lex/lex.go
@@ -128,8 +128,8 @@
tokens []Token // Body of macro.
}
-// tokenize turns a string into a list of Tokens; used to parse the -D flag.
-func tokenize(str string) []Token {
+// Tokenize turns a string into a list of Tokens; used to parse the -D flag and in tests.
+func Tokenize(str string) []Token {
t := NewTokenizer("command line", strings.NewReader(str), nil)
var tokens []Token
for {
