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See undefined behaviors 17 and 18.
Consequently, in implementations that do not allow for the representation of all numbers, conversions of values between zero and FLT_MIN are undefined behavior. For example, if an implementation supports subnormal numbers the conversion is representable, if not, the behavior is undefined.
This rule does not apply to demotions of floating-point types on implementations that support signed infinity, such as IEEE 754, as all values are within range.
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