URL / format fix 1996/schweikh1/README.md

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Cody Boone Ferguson committed 2023-04-18 09:27:01 -07:00
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# Worst Abuse of the C Preprocessor
Jens Schweikhardt
DFN Network Operation Center
Schlartaeckerweg 3 (home address)
D-71384 Weinstadt
Germany
http://www.uni-stuttgart.de/People/schweikhardt/home.html
Jens Schweikhardt
DFN Network Operation Center
Schlartaeckerweg 3 (home address)
D-71384 Weinstadt
Germany
<http://www.schweikhardt.net>
## To build:
make all
```sh
make all
```
## To run:
./schweikh1
```sh
./schweikh1
```
## Try:
To find the day that Easter falls on in the current year:
```sh
./schweikh1 |grep $(date +%Y)
```
## Judges' remarks:
@@ -27,18 +39,18 @@ C Preprocessor that the judges have seen this year!
## Author's remarks:
What this program does
----------------------
### What this program does
This program is an implementation of an algorithm that calculates
the date of the Sunday following the first full moon after the
spring equinoxe. (Also known as "Easter", defined this way by the
spring equinox. (Also known as "Easter", defined this way by the
Nicaean Concilium in 325 Anno Domini.) The algorithm is attributed
to the famous mathematician Carl Friedrich Gauss ["Meyers Handbuch
ueber das Weltall", Meyer, 5th Edition, 1973, p149] and is suitable
for anni domini within the Gregorian Calendar, that is, from 1582 AD
to 2199 AD:
```
Let J be the year.
If J is from 1582 to 1699, let M be 22, let N be 2
If J is from 1700 to 1799, let M be 23, let N be 3
@@ -51,29 +63,37 @@ Let c be the modulus of J divided by 7
Let d be the modulus of (19a + M) divided by 30
Let e be the modulus of (2b + 4c + 6d + N) divided by 7
```
The interesting Sunday is either:
March 22 + d + e or
April d + e - 9 (only one of them is a valid date)
```
March 22 + d + e or
April d + e - 9 (only one of them is a valid date)
```
with the following exceptions:
April 26 must always be changed to April 19
April 25 must be changed to April 18 if d is 28 and a greater than 10
```
April 26 must always be changed to April 19
April 25 must be changed to April 18 if d is 28 and a greater than 10
```
### Example:
J = 1962, M = 24, N = 5
a = J % 19 = 5
b = J % 4 = 2
c = J % 7 = 2
d = 119 % 30 = 29
e = 191 % 7 = 2
March 53 is invalid, so the result is April 22 1962
```
J = 1962, M = 24, N = 5
a = J % 19 = 5
b = J % 4 = 2
c = J % 7 = 2
d = 119 % 30 = 29
e = 191 % 7 = 2
```
Why I think this is obfuscated
------------------------------
March 53 is invalid, so the result is April 22 1962.
### Why I think this is obfuscated
Apart from the calculation of the Easter date, the definition *and*
calculation of which are obfuscations in their own right,
@@ -101,22 +121,22 @@ Try to be as precise as can be and no one will comprehend what you mean.
#### The formula:
comprehension = 1/(2**precision)
```
comprehension = 1/(2**precision)
```
#### The interpretation:
"Say nothing and everybody will understand."
The `-I/usr/include` in the build file is needed by gcc on Solaris because
gcc's "fixed" header in gcc-lib/sparc-sun-solaris2.5/2.7.2/include/errno.h
is broken (sort of) because it has *two* identical extern
declarations of errno. This leads to an error due to the
redefinition of main. The `-I` option makes sure the working
/usr/include/errno.h is found first, which shouldn't harm on other
systems.
`gcc`'s "fixed" header in `gcc-lib/sparc-sun-solaris2.5/2.7.2/include/errno.h`
is broken (sort of) because it has *two* identical extern declarations of errno.
This leads to an error due to the redefinition of main. The `-I` option makes
sure the working /usr/include/errno.h is found first, which shouldn't cause any
problems on other systems.
Usage
-----
### Usage
The program is run without arguments. It prints all dates in order.