| // +build ignore |
| |
| // Copyright 2014 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. |
| |
| /* |
| This file contains the code to check for suspicious shifts. |
| */ |
| |
| package main |
| |
| import ( |
| "go/ast" |
| "go/constant" |
| "go/token" |
| "go/types" |
| ) |
| |
| func init() { |
| register("shift", |
| "check for useless shifts", |
| checkShift, |
| binaryExpr, assignStmt) |
| } |
| |
| func checkShift(f *File, node ast.Node) { |
| if f.dead[node] { |
| // Skip shift checks on unreachable nodes. |
| return |
| } |
| |
| switch node := node.(type) { |
| case *ast.BinaryExpr: |
| if node.Op == token.SHL || node.Op == token.SHR { |
| checkLongShift(f, node, node.X, node.Y) |
| } |
| case *ast.AssignStmt: |
| if len(node.Lhs) != 1 || len(node.Rhs) != 1 { |
| return |
| } |
| if node.Tok == token.SHL_ASSIGN || node.Tok == token.SHR_ASSIGN { |
| checkLongShift(f, node, node.Lhs[0], node.Rhs[0]) |
| } |
| } |
| } |
| |
| // checkLongShift checks if shift or shift-assign operations shift by more than |
| // the length of the underlying variable. |
| func checkLongShift(f *File, node ast.Node, x, y ast.Expr) { |
| if f.pkg.types[x].Value != nil { |
| // Ignore shifts of constants. |
| // These are frequently used for bit-twiddling tricks |
| // like ^uint(0) >> 63 for 32/64 bit detection and compatibility. |
| return |
| } |
| |
| v := f.pkg.types[y].Value |
| if v == nil { |
| return |
| } |
| amt, ok := constant.Int64Val(v) |
| if !ok { |
| return |
| } |
| t := f.pkg.types[x].Type |
| if t == nil { |
| return |
| } |
| b, ok := t.Underlying().(*types.Basic) |
| if !ok { |
| return |
| } |
| var size int64 |
| switch b.Kind() { |
| case types.Uint8, types.Int8: |
| size = 8 |
| case types.Uint16, types.Int16: |
| size = 16 |
| case types.Uint32, types.Int32: |
| size = 32 |
| case types.Uint64, types.Int64: |
| size = 64 |
| case types.Int, types.Uint: |
| size = uintBitSize |
| case types.Uintptr: |
| size = uintptrBitSize |
| default: |
| return |
| } |
| if amt >= size { |
| ident := f.gofmt(x) |
| f.Badf(node.Pos(), "%s (%d bits) too small for shift of %d", ident, size, amt) |
| } |
| } |
| |
| var ( |
| uintBitSize = 8 * archSizes.Sizeof(types.Typ[types.Uint]) |
| uintptrBitSize = 8 * archSizes.Sizeof(types.Typ[types.Uintptr]) |
| ) |