## To build:
```
make all
```
## To use:
```
./schweikh1
```
## Try:
To find the day that Easter falls on in the current year and to show all Easter
dates from 1582 to 2199:
```
./try.sh
```
## Judges' remarks:
Look at the source. There is something very odd going on here.
Where does the real code come from if everything is a C pre-processor
statement?
Clearly this is either the Best Use or the Worst Abuse of the
C Preprocessor that the judges have seen this year!
## Author's remarks:
### 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 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](https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss) ["Meyers Handbuch
ueber das Weltall" 'Handbook About Space', Meyer, 5th Edition, 1973, p149] and is suitable
for anni domini within the [Gregorian
Calendar](https://en.wikipedia.org/wiki/Gregorian_calendar), that is, from ad 1582
to ad 2199:
> Let `J` be the year.
> If `J` is from `1582` to `1699`, let `M` be `22` and `N` be `2`.
> If `J` is from `1700` to `1799`, let `M` be `23` and `N` be `3`.
> If `J` is from `1800` to `1899`, let `M` be `23` and `N` be `4`.
> If `J` is from `1900` to `2099`, let `M` be `24`, let `N` be `5`.
> If `J` is from `2100` to `2199`, let `M` be `24`, let `N` be `6`.
> Let `a` be the modulus of `J` divided by `19`.
> Let `b` be the modulus of `J` divided by `4`.
> 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 (only one of them is a valid date):
> March `22 + d + e`; or
> April `d + e - 9`
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` is 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.
### 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,
obfuscation lurks in many places. Look at those macro identifiers.
What can be more obvious than a program that explicitly mentions the
grammatical constructs it is composed of? If you look at K&RII A.9.3
you will find that a compound statement consists of an opening brace
followed by a declaration list followed by a semicolon followed by a
statement list followed by another semicolon and a closing brace.
Nobody can learn that by heart so I gently remind the reader by
defining a macro that expresses this clearly (line 25). This goes up
to the definition of a translation unit. Unfortunately, due to the
IOCCC's size restrictions, I had to abbreviate some syntactic
elements. `ae` actually reads "assignment expression". I had to stop
at some arbitrary point, so don't waste your time trying to find out
how preprocessing tokens form type qualifier lists, cast expressions
or direct abstract declarators. Assuming the reader knows about
these easy to remember language elements is justified in my opinion.
### The moral:
Try to be as precise as can be and no one will comprehend what you mean.
#### The formula:
```
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 cause any
problems on other systems.
### Usage:
The program is run without arguments. It prints all dates in order.