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16C internal floating point format?
04-06-2021, 02:37 PM
Post: #7
RE: 16C internal floating point format?
BTW, slight correction - I meant big-endian. The internal format is rather delightful - if anyone's curious, here's my description:

Code:
///
/// Stored in what I think is the 16C's internal format
///
/// This format is interesting.  It's big-endian BCD.  The mantissa is
/// sign-magnitude, with the sign in a nybble that is 0 for positive, and
/// 9 for negative.  The exponent is 1000's complement BCD, with a magnitude
/// between 0 and 99 (inclusive).  So it looks like:
///
///      smmmmmmmmmmeee
///
/// s = mantissa sign (0/9)
/// m = mantissa magnitude
/// e = exponent (1 is 001, -1 is 0x999, -2 is 0x998, etc)
///
/// The most significant digit of the mantissa is always non-zero.  In other words,
/// 0.1e-99 underflows to zero.  The mantissa is NOT stored in complement form.  So, a
/// mantissa of -4.2 is 0x94200000000.
///
/// Note that I didn't refer to a ROM image to figure this out, or anything
/// like that.  I just asked what the behavior of the real calculator is
/// for a couple of data points.
/// cf. https://www.hpmuseum.org/forum/thread-16595-post-145554.html#pid145554
///
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RE: 16C internal floating point format? - billf - 04-06-2021 02:37 PM
New 16C simulator - alpha on web - billf - 05-01-2021, 10:19 PM



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