bpo-29962: add math.remainder #950

mdickinson · 2017-04-01T14:38:51Z

Add IEEE 754-style remainder operation.

marco-buttu · 2017-04-01T14:50:26Z

Doc/library/math.rst

@@ -175,6 +175,27 @@ Number-theoretic and representation functions
   of *x* and are floats.


+.. function:: remainder(x, y)
+
+   Return the IEEE 754-style remainder of ``x`` with respect to ``y``. For


There is a bit of inconsistency in the file, but I see that in general the parameters do not have a code markup but italic: x and y instead of x and y.
I also see in general there are two whitespaces after the period.

Thanks. Fix on the way.

serhiy-storchaka · 2017-04-01T15:10:29Z

Doc/library/math.rst

@@ -175,6 +175,27 @@ Number-theoretic and representation functions
   of *x* and are floats.


+.. function:: remainder(x, y)
+
+   Return the IEEE 754-style remainder of ``x`` with respect to ``y``. For


Parameters usually are formatted with italic. *x* and *y*.

serhiy-storchaka · 2017-04-01T15:11:24Z

Doc/library/math.rst

@@ -175,6 +175,27 @@ Number-theoretic and representation functions
   of *x* and are floats.


+.. function:: remainder(x, y)


Shouldn't it be named remainder_near as decimal.remainder_near?

That's not clear to me: see discussion in the bpo issue.

serhiy-storchaka · 2017-04-01T15:13:02Z

Doc/library/math.rst

+   Return the IEEE 754-style remainder of ``x`` with respect to ``y``. For
+   finite ``x`` and finite nonzero ``y``, this is the difference ``x - n*y``,
+   where ``n`` is the closest integer to the exact value of the quotient ``x /
+   y``. If ``x / y`` is exactly halfway between two consecutive integers, the


Sentences are separated by two spaces in this file.

Thanks. I think I caught all the single spaces.

serhiy-storchaka · 2017-04-01T15:14:22Z

Doc/library/math.rst

+   nearest *even* integer is used for ``n``. The remainder ``r = remainder(x,
+   y)`` thus always satisfies ``abs(r) <= 0.5 * abs(y)``.
+
+   Special cases follow IEEE 754: in particular, ``remainder(x, math.inf)`` is


And remainder(x, -math.inf)?

serhiy-storchaka · 2017-04-01T15:19:22Z

Doc/whatsnew/3.7.rst

+math
+----
+
+New ``remainder`` function, implementing the IEEE 754-style remainder


Maybe make it a reference? :func:'~math.remainder'?

serhiy-storchaka · 2017-04-01T15:33:25Z

Modules/mathmodule.c

+        }
+        else {
+            assert(m == c);
+            r = m - 2.0 * fmod(0.5 * (absx - m), absy);


Could you add any comment?

mdickinson · 2017-04-01T15:50:39Z

The coverage complaint seems to be because the line

self.fail("Expected a NaN, got {!r}.".format(value))

in the tests isn't being covered, and that's because none of the tests are failing. I'm not sure what to do about that.

serhiy-storchaka · 2017-04-01T15:49:03Z

Doc/whatsnew/3.7.rst

@@ -111,6 +111,12 @@ Serhiy Storchaka in :issue:`28682`.)
 Added support for :ref:`file descriptors <path_fd>` in :func:`~os.scandir`
 on Unix.  (Contributed by Serhiy Storchaka in :issue:`25996`.)

+math


math should be between locale and os.

Whoops, so it should. Thanks!

…pite of possible rounding error.

SylvainDe

Small questions about the tests

SylvainDe · 2017-04-02T17:26:37Z

Lib/test/test_math.py

+        # triples (x, y, remainder(x, y)) in hexadecimal form.
+        testcases = [
+            # Remainders modulo 1, showing the ties-to-even behaviour.
+            '-4.0 1 -0.0',


Any reason for using strings to be splitted instead of a more natural container like tuples?

Just personal preference, really. I find the individual cases to be easier to read and write this way. Comparing:

'0x1.921fb54442d18p+0 0x1.921fb54442d18p+2 0x1.921fb54442d18p+0', '-1.4 -0.c 0.4',

with

('0x1.921fb54442d18p+0', '0x1.921fb54442d18p+2', '0x1.921fb54442d18p+0'), ('-1.4', '-0.c', '0.4'),

there's a lot more noise in the latter representation.

Of course, if Python had direct support for hex floating-point literals, then

(0x1.921fb54442d18p+0, 0x1.921fb54442d18p+2, 0x1.921fb54442d18p+0),

would be the obvious representation. But it doesn't. :-(

SylvainDe · 2017-04-02T17:27:16Z

Lib/test/test_math.py

+                actual = math.remainder(-x, y)
+                validate_spec(-x, y, actual)
+
+        # Special values.


Should these cases be moved into tests on their own?

Possibly. I wanted to stay (somewhat) consistent with the existing test structure, which is mostly one test method per wrapped libm function. One day it would be nice to rework test_math. But not today.

Implement math.remainder.

55f679f

mdickinson requested a review from serhiy-storchaka April 1, 2017 14:39

marco-buttu reviewed Apr 1, 2017

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serhiy-storchaka reviewed Apr 1, 2017

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Fix markup for arguments; use double spaces after period.

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serhiy-storchaka reviewed Apr 1, 2017

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mdickinson added 2 commits April 1, 2017 16:37

Mark up function reference in what's new entry.

49aaa2a

Add comment explaining the calculation in the final branch.

2b79f77

serhiy-storchaka reviewed Apr 1, 2017

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Fix out-of-order entry in whatsnew.

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serhiy-storchaka approved these changes Apr 1, 2017

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Add comment explaining why it's good enough to compare m with c, in s…

6d80fce

…pite of possible rounding error.

SylvainDe reviewed Apr 2, 2017

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brettcannon added CLA not signed and removed CLA not signed labels Apr 3, 2017

the-knights-who-say-ni added the CLA signed label Apr 3, 2017

Merge branch 'master' into enh/math-remainder

68273b6

mdickinson merged commit a0ce375 into python:master Apr 5, 2017

mdickinson deleted the enh/math-remainder branch April 5, 2017 17:34

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bpo-29962: add math.remainder #950

bpo-29962: add math.remainder #950

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		@@ -175,6 +175,27 @@ Number-theoretic and representation functions
		of x and are floats.


		.. function:: remainder(x, y)

bpo-29962: add math.remainder #950

bpo-29962: add math.remainder #950

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