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| ID | Category | Severity | Type | Date Submitted | Last Update | ||
| 0001503 | [Issue 8 drafts] Base Definitions and Headers | Editorial | Enhancement Request | 2021-08-07 20:59 | 2022-01-13 10:13 | ||
| Reporter | andras_farkas | View Status | public | ||||
| Assigned To | |||||||
| Priority | normal | Resolution | Accepted As Marked | ||||
| Status | Applied | Product Version | |||||
| Name | Andras Farkas | ||||||
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| User Reference | |||||||
| Section | math.h | ||||||
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| Final Accepted Text | Note: 0005541 | ||||||
| Summary | 0001503: Potential new M_ constants for math.h | ||||||
| Description |
There may be five useful new M_ constants to be included in the math.h header. The latest standard for C++, known as C++20, introduces a header called <numbers>, which contains many math constants, and is similar in intent to XSI's M_ constants in math.h. There's lots of overlap, but the list of M_ constants and list of constants in <numbers> do differ. Constants in both XSI and <numbers>: M_E, e M_LOG2E, log2e M_LOG10E, log10e M_LN2, ln2 M_LN10, ln10 M_PI, pi M_1_PI, inv_pi M_SQRT2, sqrt2 Constants only in XSI: M_PI_2 M_PI_4 M_2_PI M_2_SQRTPI M_SQRT1_2 Constants only in <numbers>: inv_sqrtpi (1 divided by the square root of pi, approximately 0.5641) sqrt3 (Square root of 3, approximately 1.7320) inv_sqrt3 (1 divided by the square root of 3, approximately 0.5773) egamma (Euler-Mascheroni constant, approximately 0.5772) phi (golden ratio, approximately 1.6180) References: XSI: https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/math.h.html [^] C++20 draft standard (specifically section 26.9, page 1224): https://isocpp.org/files/papers/N4860.pdf [^] P0631R8 Math Constants (The original paper on <numbers>): http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0631r8.pdf [^] Notably, this paper references XSI. I'm not a mathematician, so I'm not sure whether adding those five new constants from <numbers> would be considered useful, or considered clutter. Please chime in. Personally, I've only ever used M_PI out of all the M_ constants, but I'm glad it's there when I do use it, and I'm glad all the constants are there. |
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| Desired Action |
I'd like for people to examine the usefulness of the five new constants. If they're judged useful: Add to the section on math.h, immediately after the other M_ constants (or interspersed with them), and also XSI-marked: M_1_SQRTPI Value of 1/sqrt(pi) M_SQRT3 Value of sqrt(3) M_1_SQRT3 Value of 1/sqrt(3) M_EGAMMA Value of [lower-case gamma], Euler-Mascheroni constant M_PHI Value of [lower-case phi], ( (1 + sqrt(5))/2 ), golden ratio constant Of course, the "Value of" text would use more fitting symbols than I was able to use here, for the values. |
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| Tags | issue8 | ||||||
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(0005430) andras_farkas (reporter) 2021-08-07 21:32 |
Actually, there could be some changes to my desired action proposal. M_1_SQRT3 should certainly be M_SQRT1_3 in order to match M_SQRT1_2 M_1_SQRTPI could also be M_SQRT1_PI to match. |
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(0005431) andras_farkas (reporter) 2021-08-07 21:41 |
Thus, desiring to be consistent with the standard as it already exists, this is my new desired action: Add to the section on math.h, immediately after the other M_ constants (or interspersed with them), and also XSI-marked: M_SQRT1_PI Value of 1/sqrt(pi) M_SQRT3 Value of sqrt(3) M_SQRT1_3 Value of 1/sqrt(3) M_EGAMMA Value of [lower-case gamma], Euler-Mascheroni constant M_PHI Value of [lower-case phi], ( (1 + sqrt(5))/2 ), golden ratio constant |
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(0005541) geoffclare (manager) 2021-12-02 17:24 edited on: 2021-12-02 17:39 |
Add the requested new M_ symbolic constants to <math.h> using the names in Note: 0005431 in an order determined by the editor all with XSI shading. Also add XSI shading to (2018 edition) P288, L9745-9746 and extend the shading down to L9759 (as a single shading block). |
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(0005598) geoffclare (manager) 2022-01-13 10:13 |
While applying this bug, on seeing the updated list with the additions in place, I decided it made more sense to add the name M_1_SQRTPI from the Desired Action, instead of M_SQRT1_PI, so that it forms a consistent set with M_1_PI, M_2_PI, and M_2_SQRTPI. |
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Issue History |
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| Date Modified | Username | Field | Change |
| 2021-08-07 20:59 | andras_farkas | New Issue | |
| 2021-08-07 20:59 | andras_farkas | Name | => Andras Farkas |
| 2021-08-07 20:59 | andras_farkas | Section | => math.h |
| 2021-08-07 21:32 | andras_farkas | Note Added: 0005430 | |
| 2021-08-07 21:41 | andras_farkas | Note Added: 0005431 | |
| 2021-12-02 17:24 | geoffclare | Note Added: 0005541 | |
| 2021-12-02 17:25 | geoffclare | Final Accepted Text | => Note: 0005541 |
| 2021-12-02 17:25 | geoffclare | Status | New => Resolved |
| 2021-12-02 17:25 | geoffclare | Resolution | Open => Accepted As Marked |
| 2021-12-02 17:25 | geoffclare | Tag Attached: issue8 | |
| 2021-12-02 17:39 | geoffclare | Note Edited: 0005541 | |
| 2022-01-13 10:13 | geoffclare | Note Added: 0005598 | |
| 2022-01-13 10:13 | geoffclare | Status | Resolved => Applied |
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