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The C Standard, 6.3.1.4, paragraph 1 2 [ISO/IEC 9899:20112024], says,

When a finite value of real decimal floating type is converted to an integer type other than _Boolbool, the fractional part is discarded (i.e. , the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the behavior is undefinedthe "invalid" floating-point exception shall be raised and the result of the conversion is unspecified.

Paragraph 2 of the same subclause says,

When a value of integer type is converted to a real standard floating type, if the value being converted can be represented exactly in the new type, it is unchanged. If the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower representable value, chosen in an implementation-defined manner. If the value being converted is outside the range of values that can be represented, the behavior is undefined.

And subclause 6.3.1.5, paragraph 1+2, says,

When a value of real floating type is converted to a real floating type, if the value being converted can be represented exactly in the new type, it is unchanged.
When a value of real floating type is converted to a standard floating type, if If the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower representable value, chosen in an implementation-defined manner. If the value being converted is outside the range of values that can be represented, the behavior is undefined.

See undefined behaviors 17 and 18.

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Overflow when converting between floating point data types

Overflow when converting between integer types

Overflow when converting between unsigned integer types

Tool

Version

Checker

Description

Astrée

Include Page

	Astrée_V
	Astrée_V

Supported

, but no explicit checker

Astrée reports all potential overflows resulting from floating-point conversions.

Compass/ROSE

Can detect some violations of this rule. However, it does not flag implicit casts, only explicit ones

CodeSonar

Include Page

	CodeSonar_V
	CodeSonar_V

LANG.TYPE.IAT

Inappropriate Assignment Type

Coverity

Include Page

	Coverity_V
	Coverity_V

MISRA_CAST (needs verification)

Can detect instances where implicit float conversion is involved: implicitly converting a complex expression with integer type to floating type, implicitly converting a double expression to narrower float type (may lose precision), implicitly converting a complex expression from float to double, implicitly converting from float to double in a function argument, and so on

Helix QAC

Include Page

	Helix QAC_V
	Helix QAC_V

C4450, C4451, C4452, C4453, C4454, C4462, C4465

C++3011

Klocwork

Include Page

	Klocwork_V
	Klocwork_V

MISRA.CAST.FLOAT.WIDER
MISRA.CAST.FLOAT.INT
MISRA.CAST.INT_FLOAT
MISRA.CONV.FLOAT

LDRA tool suite

Include Page

	LDRA_V
	LDRA_V

435 S, 93 S

Partially implemented

Parasoft C/C++test

Include Page

	Parasoft_V
	Parasoft_V

MISRA2004-10_1_d

Partially implemented

Polyspace Bug Finder

Include Page

Polyspace Bug Finder_V

Float conversion overflow

Integer conversion overflow

Unsigned integer conversion overflow

CERT_C-FLP34-a
CERT_C-FLP34-b

Avoid implicit conversions from wider to narrower floating type
Avoid implicit conversions of floating point numbers from wider to narrower floating type

PC-lint Plus

Include Page