introduce zero_expr() and one_expr() for number types

[kroening]

This adds .zero_expr() and .one_expr() for integers, natural numbers, rationals and reals.

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[tautschnig]

Should we take this opportunity to deprecate exprt::is_zero and exprt::is_one? I'd like to think that e.is_zero() would better be written as e == e.type().zero_expr() (with some extra type cast of e.type() to something more specific than typet).

[kroening]

Should we take this opportunity to deprecate exprt::is_zero and exprt::is_one? I'd like to think that e.is_zero() would better be written as e == e.type().zero_expr() (with some extra type cast of e.type() to something more specific than typet).

I considered this, but that will only work when there is a canonical representation for the respective number.

This works for integers and naturals, but, for instance, not for floats, rationals and reals.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Project coverage is 78.27%. Comparing base (dd54106) to head (9fba581).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/util/mathematical_types.cpp	0.00%	16 Missing ⚠️
src/util/mathematical_types.h	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #8441      +/-   ##
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+ Coverage    78.19%   78.27%   +0.07%     
===========================================
  Files         1726     1726              
  Lines       189068   188879     -189     
  Branches     18273    18322      +49     
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  Hits        147841   147841              
+ Misses       41227    41038     -189     

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[tautschnig]

Should we take this opportunity to deprecate exprt::is_zero and exprt::is_one? I'd like to think that e.is_zero() would better be written as e == e.type().zero_expr() (with some extra type cast of e.type() to something more specific than typet).

I considered this, but that will only work when there is a canonical representation for the respective number.

This works for integers and naturals, but, for instance, not for floats, rationals and reals.

But then exprt::is_zero and exprt::is_one perhaps are also a bit questionable for those cases?

[kroening]

But then exprt::is_zero and exprt::is_one perhaps are also a bit questionable for those cases?

They are fine -- they do handle the multiple representations.