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The C Standard, 6.5.7, paragraph 4 [ISO/IEC 9899:2011], states

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In almost every case, an attempt to shift by a negative number of bits or by more bits than exist in the operand indicates a logic error. These issues are covered by INT34-C. Do not shift an expression by a negative number of bits or by greater than or equal to the number of bits that exist in the operand.

Noncompliant Code Example

This noncompliant code example performs a left shift, after verifying that the number being shifted is not negative, and the number of bits to shift is valid. The PRECISION() macro and popcount() function provide the correct precision for any integer type. (See INT35-C. Use correct integer precisions.) However, because this code does no overflow check, it can result in an unrepresentable value.

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Compliant Solution

This compliant solution eliminates the possibility of overflow resulting from a left-shift operation:

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Tool

Version

Checker

Description

Astrée

Include Page

	Astrée_V
	Astrée_V

integer-overflow

Fully checked

CodeSonar

Include Page

	CodeSonar_V
	CodeSonar_V

ALLOC.SIZE.ADDOFLOW
ALLOC.SIZE.IOFLOW
ALLOC.SIZE.MULOFLOW
ALLOC.SIZE.SUBUFLOW
MISC.MEM.SIZE.ADDOFLOW
MISC.MEM.SIZE.BAD
MISC.MEM.SIZE.MULOFLOW
MISC.MEM.SIZE.SUBUFLOW

Addition overflow of allocation size
Integer overflow of allocation size
Multiplication overflow of allocation size
Subtraction underflow of allocation size
Addition overflow of size
Unreasonable size argument
Multiplication overflow of size
Subtraction underflow of size

Coverity

Include Page

	Coverity_V
	Coverity_V

TAINTED_SCALAR

BAD_SHIFT

Implemented

LDRA tool suite

Include Page

	LDRA_V
	LDRA_V

493 S, 494 S

Partially implemented

Parasoft C/C++test

Include Page

	Parasoft_V
	Parasoft_V

BD-PB-INTOVERF, PB-66_a, PB-66_b

CERT_C-INT32-a
CERT_C-INT32-b
CERT_C-INT32-c

Avoid integer overflows
Integer overflow or underflow in constant expression in '+', '-', '*' operator
Integer overflow or underflow in constant expression in '<<' operator

Implemented

Parasoft Insure++ Runtime

Polyspace Bug Finder

Include Page