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2a45839778
Fixes #5537 Added a note that the error check for `BN_mask_bits()` depends on the internal representation that depends on the platform's word size. Included a reference to the `BN_num_bits()` function for precise bit checking. Reviewed-by: Neil Horman <nhorman@openssl.org> Reviewed-by: Tomas Mraz <tomas@openssl.org> (Merged from https://github.com/openssl/openssl/pull/24812)
73 lines
2.2 KiB
Plaintext
73 lines
2.2 KiB
Plaintext
=pod
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=head1 NAME
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BN_set_bit, BN_clear_bit, BN_is_bit_set, BN_mask_bits, BN_lshift,
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BN_lshift1, BN_rshift, BN_rshift1 - bit operations on BIGNUMs
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=head1 SYNOPSIS
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#include <openssl/bn.h>
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int BN_set_bit(BIGNUM *a, int n);
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int BN_clear_bit(BIGNUM *a, int n);
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int BN_is_bit_set(const BIGNUM *a, int n);
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int BN_mask_bits(BIGNUM *a, int n);
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int BN_lshift(BIGNUM *r, const BIGNUM *a, int n);
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int BN_lshift1(BIGNUM *r, BIGNUM *a);
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int BN_rshift(BIGNUM *r, BIGNUM *a, int n);
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int BN_rshift1(BIGNUM *r, BIGNUM *a);
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=head1 DESCRIPTION
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BN_set_bit() sets bit B<n> in B<a> to 1 (C<a|=(1E<lt>E<lt>n)>). The
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number is expanded if necessary.
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BN_clear_bit() sets bit B<n> in B<a> to 0 (C<a&=~(1E<lt>E<lt>n)>). An
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error occurs if B<a> is shorter than B<n> bits.
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BN_is_bit_set() tests if bit B<n> in B<a> is set.
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BN_mask_bits() truncates B<a> to an B<n> bit number
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(C<a&=~((~0)E<lt>E<lt>n)>). An error occurs if B<n> is negative. An error is
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also returned if the internal representation of B<a> is already shorter than
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B<n> bits. The internal representation depends on the platform's word size, and
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this error can be safely ignored. Use L<BN_num_bits(3)> to determine the exact
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number of bits if needed.
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BN_lshift() shifts B<a> left by B<n> bits and places the result in
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B<r> (C<r=a*2^n>). Note that B<n> must be nonnegative. BN_lshift1() shifts
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B<a> left by one and places the result in B<r> (C<r=2*a>).
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BN_rshift() shifts B<a> right by B<n> bits and places the result in
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B<r> (C<r=a/2^n>). Note that B<n> must be nonnegative. BN_rshift1() shifts
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B<a> right by one and places the result in B<r> (C<r=a/2>).
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For the shift functions, B<r> and B<a> may be the same variable.
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=head1 RETURN VALUES
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BN_is_bit_set() returns 1 if the bit is set, 0 otherwise.
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All other functions return 1 for success, 0 on error. The error codes
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can be obtained by L<ERR_get_error(3)>.
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=head1 SEE ALSO
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L<BN_num_bytes(3)>, L<BN_add(3)>
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=head1 COPYRIGHT
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Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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