Campbell CR850, Руководство оператора

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Section 7. Installation
143
7.7.3.9.1 Floating-Point Arithmetic
Variables and calculations are performed internally in single precision IEEE four-
byte floating point with some operations calculated in double precision.
Note Single-precision float has 24 bits of mantissa. Double precision has a 32-bit
extension of the mantissa, resulting in 56 bits of precision. Instructions that use
double precision are
AddPrecise() , Average() , AvgRun() , AvgSpa() , CovSpa() ,
MovePrecise() , RMSSpa() , StdDev() , StdDevSpa() , and Totalize() .
Floating-point arithmetic is common in many electronic, computational systems,
but it has pitfalls high-level programmers should be aware of. Several sources
discuss floating-point arithmetic thoroughly. One readily available source is the
topic
Floating Point at www.wikipedia.org. In summary, CR800 programmers
should consider at least the following:
•
Floating-point numbers do not perfectly mimic real numbers.
•
Floating-point arithmetic does not perfectly mimic true arithmetic.
•
Avoid use of equality in conditional statements. Use >= and <= instead. For
example, use
If X >= Y then do rather than If X = Y then do .
•
When programming extended-cyclical summation of non-integers, use the
AddPrecise() instruction. Otherwise, as the size of the sum increases,
fractional addends will have an ever decreasing effect on the magnitude of
the sum, because normal floating-point numbers are limited to about 7 digits
of resolution.
7.7.3.9.2 Mathematical Operations
Mathematical operations are written out much as they are algebraically. For
example, to convert Celsius temperature to Fahrenheit, the syntax is:
TempF = TempC * 1.8 + 32
Read More! To save code space while filling an array or partial array with the
same value, see CRBasic example Use of Move() to Conserve Code Space
(p. 151).
CRBasic example Use of Variable Arrays to Conserve Code Space
(p. 151)
shows
example code to convert twenty temperatures in a variable array from °C to °F.
7.7.3.9.3 Expressions with Numeric Data Types
FLOAT s, LONG s and Boolean s are cross-converted to other data types, such as
FP2 , by using "=".
Boolean from FLOAT or LONG
When a FLOAT or LONG is converted to a Boolean as shown in CRBasic
example Conversion of FLOAT / LONG to Boolean (p. 144), zero becomes false
( 0 ) and non-zero becomes true ( -1 ).