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Great points. Out of curiosity, what are some examples of modern architectures that don’t use IEEE 754 floats? Realistically, how often would one ever write cod

Great points. Out of curiosity, what are some examples of modern architectures that don’t use IEEE 754 floats? Realistically, how often would one ever write code that needs to be portable between an architecture that uses IEEE 754 and one that doesn’t? I could only imagine this ever being an issue for code that needs to be deployed to a wide variety of exotic embedded systems, which is an extremely niche case IMO.

Banana699 5y ago
>what are some examples of modern architectures that don’t use IEEE 754 floats Mainstream? I can't think of one. Googling the question yields a stackoverflow question from 2010 that lists the 5 or 6 major architectures (x86, PowerPc, SPARC, Arm,.. ) and about a dozen more as supporting x86. So it's a fairly safe assumption to make. One area where vanilla IEEE754 isn't used that immediately came to my mind is high performance ML at companies like facebook and Google, the generic range-precision tradeoff that FP offers is inefficient and they ended up designing several new formats with smaller sizes or larger ranges. Googling "Alternatives to FP in ML" or "Custom FP format <company-name>" yields a lot. Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high school algebra that FP breaks actually have significance. (imagine the well-known FP flaw "x+epsilon == x, with epsilon non-zero" playing out in these contexts.) In any case, number portability in a language like C++ is a breeze. You design a myNumber class and overload all relevant operators and that's it. Compiler will make sure to inline the calls if they're a one-line simple floating point operations, but otherwise you can freely change the implementation of the class and the calculations never look different.
- kd5bjo 5y ago
  > Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high school algebra that FP breaks actually have significance. In particular, double-entry bookkeeping (standard practice for centuries) uses the accounting equation [1] as a checksum. If the two sides of the equation are ever unequal, then there's been a mistake somewhere that needs to be corrected. If you add the same value to a large asset account and a small liability account, for example, you can run into problems: The internal rounding performed by floating point arithmetic can mean that the increase to each side of the equation is slightly different, throwing the system out of balance. [1] https://en.wikipedia.org/wiki/Accounting_equation https://en.wikipedia.org/wiki/Accounting_equation
ChrisLomont 5y ago
> what are some examples of modern architectures that don’t use IEEE 754 floats? Lots of medical devices support floating point format from IEEE-11073 instead. I'd guess there are a significant number of them in existence and they need to be done well.
exmadscientist 5y ago
In addition to sibling comments, two more oddballs are MSP430 floats and DSPs. MSP430-style floats are common in industrial automation and such, since many sensors either use or used to use MSP430s to collect data. And, of course, in that field, legacy carries more inertia than a 50,000-ton press.... Newer DSPs tend to use IEEE-754 floats, but this was not always the case. Older DSPs used every trick in the book to go faster, and "compatibility with standard floating-point formats" was never in their product requirements. So you can guess at what manner of horrors came out of that! Fortunately, their customers are mostly the sort of people who (1) didn't mind changing to standard floats, since it's not like things were stable before; and (2) are very, very comfortable writing this stuff directly in assembly. So they definitely know whether their architecture has an instruction to take the absolute value, needs a short branching program, or just needs a single bit-operation.

Banana699 5y ago

>what are some examples of modern architectures that don’t use IEEE 754 floats Mainstream? I can't think of one. Googling the question yields a stackoverflow question from 2010 that lists the 5 or 6 major architectures (x86, PowerPc, SPARC, Arm,.. ) and about a dozen more as supporting x86. So it's a fairly safe assumption to make. One area where vanilla IEEE754 isn't used that immediately came to my mind is high performance ML at companies like facebook and Google, the generic range-precision tradeoff that FP offers is inefficient and they ended up designing several new formats with smaller sizes or larger ranges. Googling "Alternatives to FP in ML" or "Custom FP format <company-name>" yields a lot. Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high school algebra that FP breaks actually have significance. (imagine the well-known FP flaw "x+epsilon == x, with epsilon non-zero" playing out in these contexts.) In any case, number portability in a language like C++ is a breeze. You design a myNumber class and overload all relevant operators and that's it. Compiler will make sure to inline the calls if they're a one-line simple floating point operations, but otherwise you can freely change the implementation of the class and the calculations never look different.

kd5bjo 5y ago
> Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high school algebra that FP breaks actually have significance. In particular, double-entry bookkeeping (standard practice for centuries) uses the accounting equation [1] as a checksum. If the two sides of the equation are ever unequal, then there's been a mistake somewhere that needs to be corrected. If you add the same value to a large asset account and a small liability account, for example, you can run into problems: The internal rounding performed by floating point arithmetic can mean that the increase to each side of the equation is slightly different, throwing the system out of balance. [1] https://en.wikipedia.org/wiki/Accounting_equation https://en.wikipedia.org/wiki/Accounting_equation

ChrisLomont 5y ago

> what are some examples of modern architectures that don’t use IEEE 754 floats? Lots of medical devices support floating point format from IEEE-11073 instead. I'd guess there are a significant number of them in existence and they need to be done well.

exmadscientist 5y ago

In addition to sibling comments, two more oddballs are MSP430 floats and DSPs. MSP430-style floats are common in industrial automation and such, since many sensors either use or used to use MSP430s to collect data. And, of course, in that field, legacy carries more inertia than a 50,000-ton press.... Newer DSPs tend to use IEEE-754 floats, but this was not always the case. Older DSPs used every trick in the book to go faster, and "compatibility with standard floating-point formats" was never in their product requirements. So you can guess at what manner of horrors came out of that! Fortunately, their customers are mostly the sort of people who (1) didn't mind changing to standard floats, since it's not like things were stable before; and (2) are very, very comfortable writing this stuff directly in assembly. So they definitely know whether their architecture has an instruction to take the absolute value, needs a short branching program, or just needs a single bit-operation.