What is the layout of the VAX floating point format?
The VAX floating point format is derived from one of the PDP-11 FP formats, which helps explain its strange layout. There are four formats defined: F 32- bit single-precision, D and G 64-bit double-precision and H 128-bit quadruple precision. For all formats, the lowest addressed 16-bit “word” contains the sign and exponent (and for other than H, some of the most significant fraction bits). Each successive higher- addressed word contains the next 16 lesser-significant fraction bits. Bit 15 of the first word is the sign, 1 for negative, 0 for positive. Zero is represented by a biased exponent value of zero and a sign of zero; the fraction bits are ignored (but on Alpha, non- zero fraction bits in a zero value cause an error.) A value with biased exponent zero and sign bit 1 is a “reserved operand” – touching it causes an error – fraction bits are ignored. There are no minus zero, infinity, denormalized or NaN values. For all formats, the fraction is normalized and the radix point assume
