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document.writeln(Math.floor(43.9));
produces 43 in the browser.
document.writeln(Math.floor(43.9999));
produces 43
document.writeln(Math.floor(43.999999999999));
again 43
However,
document.writeln(Math.floor(43.99999999999999));
produces 44.
The magic number of 9's after the decimal point seems to be 15*.
Why is this?
Furthermore, Does the Math.floor function accept the number as a number object, or a number value?
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The Math.floor() function always rounds down and returns the largest integer less than or equal to a given number.
trunc rounds down a number to an integer towards 0 while Math. floor rounds down a number to an integer towards -Infinity . As illustrated with the following number line, the direction will be the same for a positive number while for a negative number, the directions will be the opposite.
The FLOOR. MATH function rounds a number down to the nearest integer or a multiple of specified significance, with negative numbers rounding toward or away from zero depending on the mode.
The primary reason Math. floor is slower (where it actually is--in some tests I've done it's faster) is that it involves a function call.
The IEEE 754 double-precision binary floating-point format (which is what JavaScript uses for its Number type) gives you a precision of 15 - 17 significant decimal digits.
This gives from 15 - 17 significant decimal digits precision. If a decimal string with at most 15 significant decimal is converted to IEEE 754 double precision and then converted back to the same number of significant decimal, then the final string should match the original; and if an IEEE 754 double precision is converted to a decimal string with at least 17 significant decimal and then converted back to double, then the final number must match the original [1].
Source: http://en.wikipedia.org/wiki/Double-precision_floating-point_format#IEEE_754_double-precision_binary_floating-point_format:_binary64
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