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

Application Level Programmers’ Model
elsif IsOnes(exp) then
if IsZero(frac) then
type = FPType_Infinity; value = 2^1000000;
else
type = if frac == ‘1’ then FPType_QNaN else FPType_SNaN;
value = 0.0;
else
type = FPType_Nonzero; value = 2^(UInt(exp)-127) * (1.0 + UInt(frac) * 2^-23));
else // N == 64
sign = fpval;
exp = fpval;
frac = fpval;
if IsZero(exp) then
// Produce zero if value is zero or flush-to-zero is selected.
if IsZero(frac) || fpscr_val == ‘1’ then
type = FPType_Zero; value = 0.0;
if !IsZero(frac) then // Denormalized input flushed to zero
FPProcessException(FPExc_InputDenorm, fpscr_val);
else
type = FPType_Nonzero; value = 2^-1022 * (UInt(frac) * 2^-52);
elsif IsOnes(exp) then
if IsZero(frac) then
type = FPType_Infinity; value = 2^1000000;
else
type = if frac == ‘1’ then FPType_QNaN else FPType_SNaN;
value = 0.0;
else
type = FPType_Nonzero; value = 2^(UInt(exp)-1023) * (1.0 + UInt(frac) * 2^-52));
if sign == ‘1’ then value = -value;
return (type, sign, value);
Floating-point exception and NaN handling
The FPProcessException() procedure checks whether a floating-point exception is trapped, and handles it
accordingly:
enumeration FPExc (FPExc_InvalidOp, FPExc_DivideByZero, FPExc_Overflow,
FPExc_Underflow, FPExc_Inexact, FPExc_InputDenorm};
// FPProcessException()
// ====================
//
// The ‘fpscr_val’ argument supplies FPSCR control bits. Status information is
// updated directly in the FPSCR where appropriate.
FPProcessException(FPExc exception, bits(32) fpscr_val)
// Get appropriate FPSCR bit numbers
case exception of
when FPExc_InvalidOp enable = 8; cumul = 0;
when FPExc_DivideByZero enable = 9; cumul = 1;
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A2-49