From 927df414819f236b900f9f0d925b1a6a9385c115 Mon Sep 17 00:00:00 2001 From: zlg Date: Thu, 4 Apr 2013 06:12:40 -0500 Subject: Solve Exercise 2-8: rightrot() --- ch2/2-08_rightrot.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 ch2/2-08_rightrot.c (limited to 'ch2') diff --git a/ch2/2-08_rightrot.c b/ch2/2-08_rightrot.c new file mode 100644 index 0000000..7b157a3 --- /dev/null +++ b/ch2/2-08_rightrot.c @@ -0,0 +1,52 @@ +#include + +/* The C Programming Language: 2nd Edition + * + * Exercise 2-8: Write a function rightrot(x,n) that returns the value of the + * integer x rotated to the right by n bit positions. + * + * Answer: The problem is a little ambiguous. If we're just moving the bits to + * the right n times, then the solution is a while loop combined with >>, which + * I think is much too easy. So I'm going with what I think it is: wrapping the + * bits around when they've reached the rightmost bit. It's more interesting + * and a _bit_ more difficult. Oh I kill me sometimes, ha. + * + * The trick is to determine whether masking the rightmost bit off changes the + * number that x is. If it does, then it's clear that the leftmost bit needs + * to be 1, but only after we've right-shifted x to accomodate. This requires + * a local mask variable. + * + * Due to the way shifting works, I have to establish the mask as ~0 first. + * Further bit manipulation must be done in a second statement, I assume + * because the ~ operator changes the bits that are filled in when you shift, + * too. This screws with our manipulation, so either my solution is + * suboptimal or it's just a side effect of the arithmetic. + */ + +unsigned rightrot(unsigned x, unsigned n) { + unsigned mask = ~0; + /* For some reason, I can't assign this value all at once. + * I have to assign it to all-ones, then use a separate + * statement to mess with it again... + */ + mask = ~(mask >> 1); + while (n > 0) { + /* If x is different after masking the last bit, there's a 1 in the far + * right bit and we know we need a 1 at the far left */ + if (x > (x & (~0 << 1))) { + x = x >> 1; + x = x | mask; + } else { + x = x >> 1; + } + n--; + } + return x; +} + +int main() { + printf("rightrot(3052, 3) produces %u\n", rightrot(3052, 3)); + printf("rightrot(1, 1) produces %u\n", rightrot(1, 1)); + printf("rightrot(4096, 4) produces %u\n", rightrot(4096, 4)); + return 0; +} -- cgit v1.2.3-54-g00ecf ash/log/?h=next&id=b2d47d2ca978e2cd62be4cb6fe0471598427b8b7&showmsg=1&follow=1'>root/src/vgstash/__init__.py (unfollow)
AgeCommit message (Collapse)AuthorFilesLines
2018-09-08Add remaining filters to vgstash packagezlg1-2/+11
2018-09-04Update LICENSE to match setup.pyzlg1-80/+67
Whoops.
2018-09-03Branch off from master with pytest, tox, clickzlg16-778/+779
This commit is huge, but contains everything needed for a "proper" build system built on pytest + tox and a CLI built with click. For now, this branch will contain all new vgstash development activity until it reaches feature parity with master. The CLI is installed to pip's PATH. Only the 'init', 'add', and 'list' commands work, with only two filters. This is pre-alpha software, and is therefore not stable yet.
2018-03-18Flesh out filter types and ownership statuszlg3-82/+144
It's time for a refactor to a module; the functionality and interface are clashing.
2018-03-18README.mdown: break line correctlyzlg1-1/+1
2018-03-18add 'playlog' list filterzlg2-2/+9
This filter is used to get an idea of which games you're currently playing through, so you can prioritize games to play when you're bored and detect it when you've beaten a game but haven't marked it as such.
2018-03-13Update helpers a bitzlg1-2/+9
At present, user modification is needed to make these seamless. vgup() may need to be axed in favor of telling the user to make an alias.
2018-03-13Make VGSTASH_DB_LOCATION point to a filezlg2-21/+20
It used to point to a directory, which would then look for .vgstash.db. This behavior was kind of backwards and I don't remember why I did it that way. This change gives users more control over where they put their DB. Be sure to update your environment variable if you have it set!
2016-11-18Remove settings from helpers.shZe Libertine Gamer1-5/+0
Sourcing them in .bash_profile screws up login if they're set.
2016-11-15Correct phrasing in README.Ze Libertine Gamer1-4/+4
2016-11-13DerpZe Libertine Gamer1-0/+1
2016-11-03Improve error handling in shell scriptsZe Libertine Gamer4-3/+23
2016-10-24Correct run_again, add recursionZe Libertine Gamer1-0/+4
Loops and functions -- oh my, what a useful combination. :)
2016-10-21Add quotes to correct behavior for arglistZe Libertine Gamer1-1/+1
2016-10-14updater.sh: add recursion, error handlingZe Libertine Gamer1-43/+101
2016-10-14Correct pipe-handling behaviorZe Libertine Gamer1-1/+9
2016-10-12Clarify a method to move between platformsZe Libertine Gamer1-2/+5
Also correct a typo.