On Wed, Oct 30, 2019 at 09:03:49AM +0100, Robert M. Münch via Digitalmars-d-learn wrote: > On 2019-10-29 17:43:47 +0000, H. S. Teoh said: > > > On Tue, Oct 29, 2019 at 04:54:23PM +0000, ixid via Digitalmars-d-learn > > wrote: > > > On Tuesday, 29 October 2019 at 16:11:45 UTC, Daniel Kozak wrote: > > > > On Tue, Oct 29, 2019 at 5:09 PM Daniel Kozak <kozz...@gmail.com> wrote: > > > > > > > > AFAIK dmd use real for floating point operations instead of > > > > double > > > > > > Given x87 is deprecated and has been recommended against since > > > 2003 at the latest it's hard to understand why this could be seen > > > as a good idea. > > > > Walter talked about this recently as one of the "misses" in D (one > > of the things he predicted wrongly when he designed it). > > Why should the real type be a wrong decision? Maybe the code > generation should be optimized if all terms are double to avoid x87 > but overall more precision is better for some use-cases.
It wasn't a wrong *decision* per se, but a wrong *prediction* of where the industry would be headed. Walter was expecting that people would move towards higher precision, but what with SSE2 and other such trends, and the general neglect of x87 in hardware developments, it appears that people have been moving towards 64-bit doubles rather than 80-bit extended. Though TBH, my opinion is that it's not so much neglecting higher precision, but a general sentiment of the recent years towards standardization, i.e., to be IEEE-compliant (64-bit floating point) rather than work with a non-standard format (80-bit x87 reals). I also would prefer to have higher precision, but it would be nicer if that higher precision was a standard format with guaranteed semantics that isn't dependent upon a single vendor or implementation. > I'm very happpy it exists, and x87 too because our app really needs > this extended precision. I'm not sure what we would do if we only had > doubles. > > I'm not aware of any 128 bit real implementations done using SIMD > instructions which get good speed. Anyone? [...] Do you mean *simulated* 128-bit reals (e.g. with a pair of 64-bit doubles), or do you mean actual IEEE 128-bit reals? 'cos the two are different, semantically. I'm still longing for 128-bit reals (i.e., actual IEEE 128-bit format) to show up in x86, but I'm not holding my breath. In the meantime, I've been looking into arbitrary-precision float libraries like libgmp instead. It's software-simulated, and therefore slower, but for certain applications where I want very high precision, it's the currently the only option. T -- If Java had true garbage collection, most programs would delete themselves upon execution. -- Robert Sewell
