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Footnote 160 says a cast may be used to remove extra range and precision from the return expression. This means that a predictable program must have casts on all floating-point function calls (except where the function directly feeds an operator-like assignment that implies the conversion). With type-generic math (tgmath), the programmer has to reason through the tgmath resolution rules to determine which casts to apply. These are significant obstacles to writing predictable code.

NOTE: Note that WG14 voted to include the following text in the C Standard [ISO/IEC 9899:2011]. It impacts only implementations that implement the optional Annex F, "IEC 60559 Floating-Point Arithmetic."

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float calcPercentage(float value) {
  return (float)(value * 0.1f);
}

void floatRoutine(void) {
  float value = 99.0f;
  long double percentage;

  percentage = calcPercentage(value);
}

Compliant Code Example (

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Alternative)

Unfortunately, not all compilers honor casts. In this case, the range and precision must be forced by assignment to a variable of the correct type. This compliant solution forces the assignment by type-qualifying result as volatile and assigning the result of the floating-point operation to result before returning it:

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Related Vulnerabilities

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