[REBOL] rounding and precision
From: lmecir::mbox::vol::cz at: 5-Apr-2002 9:24
Hi all,
I was experimenting with rounding again and noticed this:
mod1: function [
{Compute a non-negative remainder}
a [number!]
b [number!]
] [r] [
either negative? r: a // b [r + abs b] [r]
]
mod2: func [
{Compute a non-negative remainder}
a [number!]
b [number!]
] [
a // b + (abs b) // b
]
round: func [
{Round a number}
n [number!]
/to
factor [number!] {the number a multiply of which to round to}
] [
if not to [factor: 1]
n: 0.5 * factor + n
n - mod n factor
]
foreach f [mod1 mod2] [
mod: get f
print ["mod:" mold :mod]
foreach num [-5e-3 -4e-3 -3e-3 -2e-3 -1e-3 0 1e-3 2e-3 3e-3 4e-3] [
print ["num:" num "rounded:" round/to num 1e-2]
]
]
The results are:
mod: func [
"Compute a non-negative remainder"
a [number!]
b [number!] /local r][
either negative? r: a // b [r + abs b] [r]
]
num: -5E-3 rounded: 0
num: -4E-3 rounded: 0
num: -3E-3 rounded: 0
num: -2E-3 rounded: 0
num: -1E-3 rounded: 0
num: 0 rounded: 0
num: 1E-3 rounded: 0
num: 2E-3 rounded: 0
num: 3E-3 rounded: 0
num: 4E-3 rounded: 0
mod: func [
"Compute a non-negative remainder"
a [number!]
b [number!]
][
a // b + (abs b) // b
]
num: -5E-3 rounded: 0
num: -4E-3 rounded: 8.67361737988404E-19
num: -3E-3 rounded: 0
num: -2E-3 rounded: -8.67361737988404E-19
num: -1E-3 rounded: 0
num: 0 rounded: 8.67361737988404E-19
num: 1E-3 rounded: 0
num: 2E-3 rounded: -8.67361737988404E-19
num: 3E-3 rounded: -1.73472347597681E-18
num: 4E-3 rounded: -1.73472347597681E-18
Cheers
L
