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Sun Studio 12: C User's Guide

F.2.3 Exceptional Values

float and double numbers are said to contain a “hidden,” or implied, bit, providing for one more bit of precision than would otherwise be the case. In the case of long double, the leading bit is implicit (SPARC) or explicit (x86); this bit is 1 for normal numbers, and 0 for subnormal numbers.

Table F–10 float Representations

normal number (0<e<255): 

(-1)Sign2 (exponent- 127)1.f

subnormal number 

(e=0, f!=0): 

(-1)Sign2 (-126)0.f

zero (e=0, f=0): 

(-1)Sign0.0

signaling NaN 

s=u, e=255(max); f=.0uuu-uu; at least one bit must be nonzero 

quiet NaN 

s=u, e=255(max); f=.1uuu-uu 

Infinity 

s=u, e=255(max); f=.0000-00 (all zeroes) 

Table F–11 double Representations

normal number (0<e<2047): 

(-1)Sign2 (exponent- 1023)1.f

subnormal number (e=0, f!=0): 

(-1)Sign2 (-1022)0.f

zero (e=0, f=0): 

(-1)Sign0.0

signaling NaN 

s=u, e=2047(max); f=.0uuu-uu; at least one bit must be nonzero 

quiet NaN 

s=u, e=2047(max); f=.1uuu-uu 

Infinity 

s=u, e=2047(max); f=.0000-00 (all zeroes) 

Table F–12 long double Representations

normal number (0<e<32767): 

(-1)Sign2 (exponent- 16383)1.f

subnormal number (e=0, f!=0): 

(-1)Sign2 (-16382)0.f

zero (e=0, f=0): 

(-1)Sign0.0

signaling NaN 

s=u, e=32767(max); f=.0uuu-uu; at least one bit must be nonzero 

quiet NaN 

s=u, e=32767(max); f=.1uuu-uu 

Infinity 

s=u, e=32767(max); f=.0000-00 (all zeroes)