363 lines
10 KiB
Factor
363 lines
10 KiB
Factor
! Copyright (C) 2008 Doug Coleman.
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! See http://factorcode.org/license.txt for BSD license.
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USING: help.markup help.syntax math sequences ;
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IN: math.bitwise
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HELP: bitfield
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{ $values { "values..." "a series of objects" } { "bitspec" "an array" } { "n" integer } }
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{ $description "Constructs an integer from a series of values on the stack together with a bit field specifier, which is an array whose elements have one of the following shapes:"
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{ $list
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{ { $snippet "{ constant shift }" } " - the resulting bit field is bitwise or'd with " { $snippet "constant" } " shifted to the right by " { $snippet "shift" } " bits" }
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{ { $snippet "{ word shift }" } " - the resulting bit field is bitwise or'd with " { $snippet "word" } " applied to the top of the stack; the result is shifted to the right by " { $snippet "shift" } " bits" }
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{ { $snippet "shift" } " - the resulting bit field is bitwise or'd with the top of the stack; the result is shifted to the right by " { $snippet "shift" } " bits" }
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}
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"The bit field specifier is processed left to right, so stack values should be supplied in reverse order." }
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{ $examples
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"Consider the following specification:"
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{ $list
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{ "bits 0-10 are set to the value of " { $snippet "x" } }
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{ "bits 11-14 are set to the value of " { $snippet "y" } }
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{ "bit 15 is always on" }
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{ "bits 16-20 are set to the value of " { $snippet "fooify" } " applied to " { $snippet "z" } }
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}
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"Such a bit field construction can be specified with a word like the following:"
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{ $code
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": baz-bitfield ( x y z -- n )"
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" {"
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" { fooify 16 }"
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" { 1 15 }"
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" 11"
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" 0"
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" } ;"
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}
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} ;
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HELP: bits
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{ $values { "m" integer } { "n" integer } { "m'" integer } }
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{ $description "Keep only n bits from the integer m." }
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{ $example "USING: math.bitwise prettyprint ;" "HEX: 123abcdef 16 bits .h" "cdef" } ;
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HELP: bitroll
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{ $values { "x" integer } { "s" "a shift integer" } { "w" "a wrap integer" } { "y" integer }
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}
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{ $description "Roll n by s bits to the left, wrapping around after w bits." }
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{ $examples
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{ $example "USING: math.bitwise prettyprint ;" "1 -1 32 bitroll .b" "10000000000000000000000000000000" }
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{ $example "USING: math.bitwise prettyprint ;" "HEX: ffff0000 8 32 bitroll .h" "ff0000ff" }
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} ;
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HELP: bit-clear?
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{ $values
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{ "x" integer } { "n" integer }
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{ "?" "a boolean" }
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}
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{ $description "Returns " { $link t } " if the nth bit is set to zero." }
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{ $examples
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: ff 8 bit-clear? ."
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"t"
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}
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{ $example "" "USING: math.bitwise prettyprint ;"
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"HEX: ff 7 bit-clear? ."
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"f"
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}
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} ;
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{ bit? bit-clear? set-bit clear-bit } related-words
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HELP: bit-count
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{ $values
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{ "x" integer }
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{ "n" integer }
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}
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{ $description "Returns the number of set bits as an integer." }
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{ $examples
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: f0 bit-count ."
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"4"
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}
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{ $example "USING: math.bitwise prettyprint ;"
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"-7 bit-count ."
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"2"
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}
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} ;
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HELP: bitroll-32
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{ $values
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{ "n" integer } { "s" integer }
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{ "n'" integer }
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}
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{ $description "Rolls the number " { $snippet "n" } " by " { $snippet "s" } " bits to the left, wrapping around after 32 bits." }
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{ $examples
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: 1 10 bitroll-32 .h"
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"400"
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}
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: 1 -10 bitroll-32 .h"
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"400000"
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}
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} ;
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HELP: bitroll-64
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{ $values
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{ "n" integer } { "s" "a shift integer" }
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{ "n'" integer }
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}
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{ $description "Rolls the number " { $snippet "n" } " by " { $snippet "s" } " bits to the left, wrapping around after 64 bits." }
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{ $examples
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: 1 10 bitroll-64 .h"
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"400"
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}
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{ $example "USING: math.bitwise prettyprint ;"
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"HEX: 1 -10 bitroll-64 .h"
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"40000000000000"
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}
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} ;
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{ bitroll bitroll-32 bitroll-64 } related-words
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HELP: clear-bit
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{ $values
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{ "x" integer } { "n" integer }
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{ "y" integer }
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}
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{ $description "Sets the nth bit of " { $snippet "x" } " to zero." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ff 7 clear-bit .h"
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"7f"
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}
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} ;
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HELP: flags
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{ $values
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{ "values" sequence }
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}
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{ $description "Constructs a constant flag value from a sequence of integers or words that output integers. The resulting constant is computed at compile-time, which makes this word as efficient as using a literal integer." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"IN: scratchpad"
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": MY-CONSTANT HEX: 1 ; inline"
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"{ HEX: 20 MY-CONSTANT BIN: 100 } flags .h"
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"25"
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}
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} ;
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HELP: mask
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{ $values
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{ "x" integer } { "n" integer }
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{ "?" "a boolean" }
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}
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{ $description "After the operation, only the bits that were set in both the mask and the original number are set." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"BIN: 11111111 BIN: 101 mask .b"
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"101"
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}
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} ;
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HELP: mask-bit
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{ $values
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{ "m" integer } { "n" integer }
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{ "m'" integer }
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}
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{ $description "Turns off all bits besides the nth bit." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ff 2 mask-bit .b"
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"100"
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}
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} ;
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HELP: mask?
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{ $values
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{ "x" integer } { "n" integer }
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{ "?" "a boolean" }
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}
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{ $description "Returns true if all of the bits in the mask " { $snippet "n" } " are set in the integer input " { $snippet "x" } "." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ff HEX: f mask? ."
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"t"
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}
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: f0 HEX: 1 mask? ."
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"f"
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}
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} ;
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HELP: on-bits
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{ $values
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{ "n" integer }
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{ "m" integer }
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}
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{ $description "Returns an integer with " { $snippet "n" } " bits set." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"6 on-bits .h"
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"3f"
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}
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"64 on-bits .h"
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"ffffffffffffffff"
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}
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} ;
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HELP: toggle-bit
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{ $values
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{ "m" integer }
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{ "n" integer }
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{ "m'" integer }
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}
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{ $description "Toggles the nth bit of an integer." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"0 3 toggle-bit .b"
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"1000"
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}
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"BIN: 1000 3 toggle-bit .b"
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"0"
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}
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} ;
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HELP: set-bit
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{ $values
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{ "x" integer } { "n" integer }
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{ "y" integer }
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}
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{ $description "Sets the nth bit of " { $snippet "x" } "." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"0 5 set-bit .h"
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"20"
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}
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} ;
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HELP: shift-mod
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{ $values
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{ "n" integer } { "s" integer } { "w" integer }
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{ "n" integer }
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}
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{ $description "" } ;
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HELP: unmask
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{ $values
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{ "x" integer } { "n" integer }
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{ "?" "a boolean" }
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}
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{ $description "Clears the bits in " { $snippet "x" } " if they are set in the mask " { $snippet "n" } "." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ff HEX: 0f unmask .h"
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"f0"
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}
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} ;
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HELP: unmask?
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{ $values
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{ "x" integer } { "n" integer }
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{ "?" "a boolean" }
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}
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{ $description "Tests whether unmasking the bits in " { $snippet "x" } " would return an integer greater than zero." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ff HEX: 0f unmask? ."
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"t"
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}
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} ;
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HELP: w*
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{ $values
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{ "int" integer } { "int" integer }
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{ "int" integer }
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}
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{ $description "Multiplies two integers and wraps the result to 32 bits." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ffffffff HEX: 2 w* ."
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"4294967294"
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}
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} ;
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HELP: w+
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{ $values
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{ "int" integer } { "int" integer }
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{ "int" integer }
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}
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{ $description "Adds two integers and wraps the result to 32 bits." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: ffffffff HEX: 2 w+ ."
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"1"
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}
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} ;
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HELP: w-
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{ $values
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{ "int" integer } { "int" integer }
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{ "int" integer }
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}
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{ $description "Subtracts two integers and wraps the result to 32 bits." }
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{ $examples
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{ $example "USING: math.bitwise kernel prettyprint ;"
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"HEX: 0 HEX: ff w- ."
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"4294967041"
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}
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} ;
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HELP: wrap
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{ $values
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{ "m" integer } { "n" integer }
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{ "m'" integer }
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}
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{ $description "Wraps an integer " { $snippet "m" } " by modding it by " { $snippet "n" } ". This word is uses bitwise arithmetic and does not actually call the modulus word, and as such can only mod by powers of two." }
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{ $examples "Equivalent to modding by 8:"
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{ $example
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"USING: math.bitwise prettyprint ;"
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"HEX: ffff 8 wrap .h"
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"7"
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}
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} ;
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ARTICLE: "math-bitfields" "Constructing bit fields"
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"Some applications, such as binary communication protocols and assemblers, need to construct integers from elaborate bit field specifications. Hand-coding this using " { $link shift } " and " { $link bitor } " results in repetitive code. A higher-level facility exists to factor out this repetition:"
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{ $subsection bitfield } ;
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ARTICLE: "math.bitwise" "Additional bitwise arithmetic"
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"The " { $vocab-link "math.bitwise" } " vocabulary provides bitwise arithmetic words extending " { $link "bitwise-arithmetic" } ". They are useful for efficiency, low-level programming, and interfacing with C libraries."
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$nl
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"Setting and clearing bits:"
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{ $subsection set-bit }
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{ $subsection clear-bit }
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"Testing if bits are set or clear:"
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{ $subsection bit? }
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{ $subsection bit-clear? }
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"Operations with bitmasks:"
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{ $subsection mask }
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{ $subsection unmask }
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{ $subsection mask? }
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{ $subsection unmask? }
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"Generating an integer with n set bits:"
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{ $subsection on-bits }
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"Counting the number of set bits:"
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{ $subsection bit-count }
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"More efficient modding by powers of two:"
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{ $subsection wrap }
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"Bit-rolling:"
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{ $subsection bitroll }
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{ $subsection bitroll-32 }
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{ $subsection bitroll-64 }
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"32-bit arithmetic:"
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{ $subsection w+ }
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{ $subsection w- }
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{ $subsection w* }
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"Bitfields:"
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{ $subsection flags }
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{ $subsection "math-bitfields" } ;
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ABOUT: "math.bitwise"
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