On 2015-12-10 17:54, Geoff Canyon wrote:
LiveCode works in 64 bit numbers, so why does
put 10000000000 * 1000000000000000000000000000000
result in
10000000000000000303786028427003666890752
which is close to the right answer, instead of some 18 digit value?
When numbers are too large to represent exactly, LiveCode automatically
shifts to using 64-bit IEEE floating point representation.
Floating-point numbers store a number in three pieces:
1) a sign bit
2) an exponent (11 bits)
3) a mantissa (52 bits)
This is a bit like writing decimal scientific notation. The "true"
value is 1.<MANTISSA> * 2^<EXPONENT>, modified by the SIGN.
This means that much much larger numbers than 2^64 can be represented in
only 64 bits, but at the cost of loss of accuracy (because the mantissa
is only 53 bits). As you've noticed, the result of your calculation is
only *close to* the right answer. It can accurately represent any
number that only requires 53 bits of precision.
See also
https://en.wikipedia.org/wiki/Double-precision_floating-point_format
Peter
--
Dr Peter Brett <peter.br...@livecode.com>
LiveCode Open Source Team
LiveCode on reddit! <https://reddit.com/r/livecode>
_______________________________________________
use-livecode mailing list
use-livecode@lists.runrev.com
Please visit this url to subscribe, unsubscribe and manage your subscription
preferences:
http://lists.runrev.com/mailman/listinfo/use-livecode
