ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

exponent == 0x7FF
fraction != 0
The value is a denormalized number and is equal to:
1 –S × 2 –1022 × (0.fraction)
Application Level Programmers’ Model
The minimum positive denormalized number is 2 –1074 , or approximately 4.941 × 10 –324 .
Optionally, denormalized numbers are flushed to zero in the VFP extension. For details see
Flush-to-zero on page A2-39.
The value is either an infinity or a NaN, depending on the fraction bits:
fraction == 0
the value is an infinity. As for single-precision, there are two infinities:
+∞ Plus infinity, when S==0
-∞ Minus infinity, when S==1.
fraction != 0
The value is a NaN, and is either a quiet NaN or a signaling NaN.
In the VFP architecture, the two types of NaN are distinguished on the basis of
their most significant fraction bit, bit [19] of the most significant word:
bit [19] == 0
The NaN is a signaling NaN. The sign bit can take any value, and
the remaining fraction bits can take any value except all zeros.
bit [19] == 1
The NaN is a quiet NaN. The sign bit and the remaining fraction bits
can take any value.
For details of the default NaN see NaN handling and the Default NaN on page A2-41.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A2-37