bitarray.html (5145B)
1 <html> 2 <head> 3 <meta name="viewport" content="width=device-width, initial-scale=1.0" /> 4 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 5 <meta http-equiv="Content-Language" content="en" /> 6 <title>skalibs: the bitarray library interface</title> 7 <meta name="Description" content="skalibs: the bitarray library interface" /> 8 <meta name="Keywords" content="skalibs c unix bitarray library libstddjb" /> 9 <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> 10 </head> 11 <body> 12 13 <p> 14 <a href="index.html">libstddjb</a><br /> 15 <a href="../libskarnet.html">libskarnet</a><br /> 16 <a href="../index.html">skalibs</a><br /> 17 <a href="//skarnet.org/software/">Software</a><br /> 18 <a href="//skarnet.org/">skarnet.org</a> 19 </p> 20 21 <h1> The <tt>bitarray</tt> library interface </h1> 22 23 <p> 24 The following functions are declared in the <tt>skalibs/bitarray.h</tt> header, 25 and implemented in the <tt>libskarnet.a</tt> or <tt>libskarnet.so</tt> library. 26 </p> 27 28 <h2> General information </h2> 29 30 <p> 31 <tt>bitarray</tt> is a set of primitives to operate efficiently on 32 large bitfields. 33 </p> 34 35 <p> 36 A bitfield is represented by a pre-allocated block of 37 <tt>unsigned char</tt>; <tt>bitarray</tt> does not care if that 38 block has been BSS-, stack- or heap-allocated. Bitfields that 39 can grow in size should be stored in a 40 <a href="stralloc.html">stralloc</a>. 41 </p> 42 43 <p> 44 Bits in a bitfield of length <em>n</em> are numbered from 0 to <em>n</em>-1. 45 </p> 46 47 <h2> Functions </h2> 48 49 <p> 50 <code> size_t bitarray_div8 (size_t n) </code> <br /> 51 Returns the minimum number of bytes needed to store a field of <em>n</em> bits. 52 53 </p> 54 55 <p> 56 <code> void bitarray_clearsetn (unsigned char *s, size_t start, size_t len, int h) </code> <br /> 57 Sets (if <em>h</em> is nonzero) or clears (if <em>h</em> is zero) 58 <em>len</em> bits in field <em>s</em>, starting at bit <em>start</em>. 59 </p> 60 61 <p> 62 <code> void bitarray_clearn (unsigned char *s, size_t start, size_t len) </code> <br /> 63 Clears <em>len</em> bits in field <em>s</em>, starting at bit <em>start</em>. 64 </p> 65 66 <p> 67 <code> void bitarray_setn (unsigned char *s, size_t start, size_t len) </code> <br /> 68 Sets <em>len</em> bits in field <em>s</em>, starting at bit <em>start</em>. 69 </p> 70 71 <p> 72 <code> int bitarray_peek (unsigned char const *s, size_t n) </code> <br /> 73 Returns the value of the <em>n</em>th bit in field <em>s</em>. 74 </p> 75 76 <p> 77 <code> void bitarray_poke (unsigned char *s, size_t n, int h) </code> <br /> 78 Sets (if <em>h</em> is nonzero) or clears (if <em>h</em> is zero) 79 the <em>n</em>th bit in field <em>s</em>. 80 </p> 81 82 <p> 83 <code> void bitarray_clear (unsigned char *s, size_t n) </code> <br /> 84 Clears the <em>n</em>th bit in field <em>s</em>. 85 </p> 86 87 <p> 88 <code> void bitarray_set (unsigned char *s, size_t n) </code> <br /> 89 Sets the <em>n</em>th bit in field <em>s</em>. 90 </p> 91 92 <p> 93 <code> int bitarray_testandpoke (unsigned char *s, size_t n, int h) </code> <br /> 94 Sets (if <em>h</em> is nonzero) or clears (if <em>h</em> is zero) 95 the <em>n</em>th bit in field <em>s</em>, 96 and returns the previous value of that bit. 97 </p> 98 99 <p> 100 <code> int bitarray_testandclear (unsigned char *s, size_t n) </code> <br /> 101 Clear the <em>n</em>th bit in field <em>s</em>, 102 and returns the previous value of that bit. 103 </p> 104 105 <p> 106 <code> int bitarray_testandset (unsigned char *s, size_t n) </code> <br /> 107 Sets the <em>n</em>th bit in field <em>s</em>, 108 and returns the previous value of that bit. 109 </p> 110 111 <p> 112 <code> size_t bitarray_first (unsigned char const *s, size_t len, int h) </code> <br /> 113 Returns the number of the first set (if <em>h</em> is nonzero) or clear 114 (if <em>h</em> is zero) bit in <em>s</em>, <em>len</em> being 115 the total number of bits. If all bits in <em>s</em> are the negation of 116 <em>h</em>, then <em>len</em> is returned. 117 </p> 118 119 <p> 120 <code> size_t bitarray_firstclear (unsigned char const *s, size_t len) </code> <br /> 121 Returns the number of the first clear bit in <em>s</em>, <em>len</em> being 122 the total number of bits. If all bits in <em>s</em> are set, <em>len</em> is returned. 123 </p> 124 125 <p> 126 <code> size_t bitarray_firstclear_skip (unsigned char const *s, size_t len, size_t skip) </code> <br /> 127 Like <tt>bitarray_firstclear</tt>, but the first <em>skip</em> bits are 128 ignored: the function cannot return less than <em>skip</em>. It is a 129 programming error if <em>skip</em> > <em>len</em>. 130 </p> 131 132 <p> 133 <code> size_t bitarray_firstset (unsigned char const *s, size_t len) </code> <br /> 134 Returns the number of the first set bit in <em>s</em>, <em>len</em> being 135 the total number of bits. If all bits in <em>s</em> are clear, <em>len</em> is returned. 136 </p> 137 138 <p> 139 <code> size_t bitarray_firstset_skip (unsigned char const *s, size_t len, size_t skip) </code> <br /> 140 Like <tt>bitarray_firstset</tt>, but the first <em>skip</em> bits are 141 ignored: the function cannot return less than <em>skip</em>. It is a 142 programming error if <em>skip</em> > <em>len</em>. 143 </p> 144 145 <p> 146 <code> size_t bitarray_countones (unsigned char const *s, size_t len) </code> <br /> 147 Returns the number of set bits in <em>s</em>, <em>len</em> being the 148 total number of bits being tested. 149 </p> 150 151 </body> 152 </html>