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+c='/* s2 - perfect hash table lookups
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+ Copyright (C) 2019 Ariadne Devos
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+
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+ This program is free software: you can redistribute it and/or modify
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+ it under the terms of the GNU General Public License as published by
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+ the Free Software Foundation, either version 3 of the License, or
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+ (at your option) any later version.
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+
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+ This program is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ GNU General Public License for more details.
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+
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+ You should have received a copy of the GNU General Public License
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+ along with this program. If not, see <http://www.gnu.org/licenses/>. */
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+/* This comment applies to both the script and code embedded in the
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+ generated output. */'
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+# This assumes the Bash shell!
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+IFS=' '
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+# * Local variables
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+# input for gperf
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+tmpgperf=""
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+# output for gperf
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+gperfout=""
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+# code to write before the generated code
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+prefix=""
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+# code to write after the generated code
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+postfix=""
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+# name of the table, set by prepare
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+table=""
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+
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+function oops() {
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+ echo -E "$1 (status code: $?)" >&2;
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+ exit 2;
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+}
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+
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+function opentmp() {
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+ # pass-by-reference
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+ local -n fd="$1"
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+ local fd="$1"
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+ local name="`mktemp`"
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+ if [ -z "$name" ]; then
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+ oops 'cannot create temporary file';
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+ fi
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+ # {fd}: allocate a file descriptor
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+ exec {fd}<>"${name}" || oops 'cannot open temporary file'
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+ # close the temporary file while it is open,
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+ # to avoid any trapping
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+ #
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+ # There is a little race window, but empty files
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+ # are small.
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+ rm "${name}"
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+}
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+
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+
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+function prepare() {
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+ table="$1"
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+ # TODO: validate ${table}
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+ # open a temporary file for gperf's input
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+ opentmp tmpgperf
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+ opentmp gperfout
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+ opentmp prefix
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+ opentmp postfix
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+ cat >&"${tmpgperf}" <<EOF
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+/* don't hide the hash table */
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+%global-table
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+/* Don't put strings into the wordlist, only offsets -- reduces memory usage */
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+%pic
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+/* Don't allow lookup tables to be modified -- facilitates static analysis,
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+ may reduce memory usage on some shared memory systems
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+ and catches accidental writes. */
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+%readonly-tables
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+%define hash-function-name ${table}_hash
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+%define lookup-function-name ${table}_lookup_ignore
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+%define string-pool-name ${table}_strings
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+/* a hash table from keywords to their value */
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+%define word-array-name ${table}_entries
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+
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+/* gperf requires the string pool offset to be named 'name'. */
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+/* This has been duplicated from <sHT/phash.h>. It will be deleted from the
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+ output. */
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+struct sHT_perfect_entry { uint_least16_t name; uint_least16_t length; uint_least32_t value; };
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+
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+%struct-type
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+%language=ANSI-C
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+
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+%{
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+$c
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+/* This is a generated file, do not edit manually! */
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+#include <sHT/phash.h>
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+/* For size_t, offsetof */
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+#include <stddef.h>
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+%}
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+%%
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+EOF
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+ [ "$?" -eq 0 ] || oops 'cannot write gperf header'
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+}
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+
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+function entry() {
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+ local name="$1"
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+ local value="$2"
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+ # - TODO: generate verification conditions for the hashing of all
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+ # keywords, for formal verification
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+ if [ -z "$name" ] || [ -z "$value" ]; then
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+ oops 'keywords and values may not be empty'
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+ fi
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+
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+ echo -E "\"${name}\", sizeof(\"${name}\") - 1, $value" >&"${tmpgperf}" || oops 'cannot write hash table entry'
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+}
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+
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+
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+function pre() {
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+ echo -E "$1" >&"$prefix" || oops 'cannot write preprocessor input'
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+}
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+
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+function post() {
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+ echo -E "$1" >&"$postfix" || oops 'cannot write preprocessor input'
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+}
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+
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+function solve() {
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+ # Generate the hash function and table
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+ # /dev/fd is recognised by Bash and exists on my
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+ # Linux box -- Debian 9. Bash doesn't have a rewind or seek builtin
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+ #
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+ # Post-process the output:
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+ # - let the 'len' argument of the hash function be a size_t
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+ # instead of unsigned int.
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+ # (Also correct the hash function output type,
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+ # and let it be inline)
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+ # - don't allocate memory for a NUL terminator
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+ # - don't emit the lookup function (static inline)
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+ # (TODO: remove completely)
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+ # - compute string offsets more according to the standard
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+ # -- with offsetof
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+ # - make sure string offsets of empty entries are within
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+ # bounds (zero offset and length)
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+ # (also, make the 'unknown' value explicit)
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+ # (this may need to be repeated multiple times in a line)
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+ # - remove the reference to strcmp
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+ # - remove the definition of sHT_perfect_entry
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+ set -o pipefail
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+ gperf < "/dev/fd/${tmpgperf}" | \
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+ sed -E \
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+ -e 's/\bunsigned int len\b/size_t len/' \
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+ -e 's/^static unsigned int$/static inline size_t/' \
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+ -e 's/(char [a-zA-Z0-9_]+_strings_str[0-9]+\[sizeof\(".*"\))\];/\1 - 1];/' \
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+ -e 's/^const struct sHT_perfect_entry \*$/static inline const struct sHT_perfect_entry \*/' \
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+ -e 's/\(int\)\(long\)&\(\(struct ([a-zA-Z0-9_]+_strings)_t \*\)0\)->\1_str([0-9]+)\b/offsetof\(struct \1_t, \1_str\2\)/' \
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+ -e ':begin s/\{-1\}/{ 0, 0, 0 }/;t begin' \
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+ -e 's/!strcmp \(str \+ 1\, s \+ 1\)/0/' \
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+ -e 's/^(struct sHT_perfect_entry) \{.*\};$/\1;/' \
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+ >&"${gperfout}"
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+ local err="$?"
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+ if [ ! "$err" -eq 0 ]; then
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+ echo -E "cannot generate hash function and table (status code: $err)"
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+ # output the test case, to ease debugging,
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+ echo -E 'Begin failed input:' >&2
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+ # The input must be rewinded!
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+ cat >&2 <"/dev/fd/${tmpgperf}"
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+ echo -E 'End failed input.' >&2
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+ exit 2;
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+ fi
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+ # Check the output:
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+ # (the input must be rewinded!)
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+ # - for switch statements (unhidden conditionals)
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+ # (these probably can be hidden)
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+ grep -E '\bswitch\b' >/dev/null < "/dev/fd/${gperfout}"
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+ case "$?" in
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+ 0) oops 'TODO: generated code gperf output contains unguarded branches' ;;
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+ 1) ;;
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+ 2) oops 'grep does not recognise unhidden conditional pattern' ;;
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+ *) oops 'unexpected grep exit status' ;;
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+ esac
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+ # Generate an exported lookup function
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+ # (Why only export a lookup function? For simpler live-patch consistency.)
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+ # The input must be rewinded!
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+ cat >&"${gperfout}" <<EOF
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+
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+static const struct sHT_perfect_table ${table}_table = {
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+ .string_pool = ${table}_strings,
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+ .values_length = sizeof(${table}_entries) / sizeof(*${table}_entries),
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+ .values = ${table}_entries,
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+};
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+
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+/* Carefully read <sHT/phash.h> before use */
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+size_t
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+${table}_lookup(const uint8_t string[], size_t length)
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+{
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+ size_t hash = ${table}_hash(string, length);
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+ return sHT_perfect_lookup(&${table}_table, string, length, hash);
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+}
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+EOF
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+ [ "$?" -eq 0 ] || oops 'cannot generate lookup function'
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+ cat < "/dev/fd/${prefix}" || oops 'cannot output prefix'
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+ cat < "/dev/fd/${gperfout}" || oops 'cannot output generated code'
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+ cat < "/dev/fd/${postfix}" || oops 'cannot output postfix'
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+}
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+
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+case "$1" in
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+--help)
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+ cat <<EOF
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+Generate perfect hash tables.
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+How to use:
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+bash ./buffer/gen-phash.sh --gen instructions.sh > output.c
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+EOF
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+ [ "$?" -eq 0 ] || oops 'cannot output help message' ;;
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+--gen)
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+ source "$2" || oops 'cannot generate hash table' ;;
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+*) oops 'unsupported option' ;;
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+esac
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Ariadne Devos