m + add man pages

Signed-off-by: Mattias Andrée <maandree@kth.se>

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+.TH LIBHASHSUM_INIT_SHAKE128_HASHER 3 libhashsum
+.SH NAME
+libhashsum_init_shake128_hasher - initialise state for SHAKE128 hashing
+
+.SH SYNOPSIS
+.nf
+#include <libhashsum.h>
+
+\fBstruct libhashsum_hasher\fP {
+	enum libhashsum_algorithm \fIalgorithm\fP;
+	const char *\fIalgorithm_string\fP;
+	size_t \fIinput_block_size\fP;
+	size_t \fIhash_size\fP;
+	unsigned char *\fIhash_output\fP;
+	unsigned char \fIsupports_non_whole_bytes\fP;
+	size_t (*\fIprocess\fP)(struct libhashsum_hasher *\fPthis\fP, const void *\fPdata\fP, size_t \fPbytes\fP);
+	int (*\fIfinalise_const\fP)(struct libhashsum_hasher *\fPthis\fP, const void *\fPdata\fP, size_t \fPbytes\fP, unsigned \fPextra_bits\fP);
+	int (*\fIfinalise\fP)(struct libhashsum_hasher *\fPthis\fP, void *\fPdata\fP, size_t \fPbytes\fP, unsigned \fPextra_bits\fP, size_t \fPsize\fP);
+	void (*\fIdestroy\fP)(struct libhashsum_hasher *\fPthis\fP);
+	union libhashsum_state { /* definition omitted */ } \fIstate\fP;
+};
+
+int \fBlibhashsum_init_shake128_hasher\fP(struct libhashsum_hasher *\fIhasher\fP, size_t \fIhashbits\fP);
+.fi
+.PP
+Link with
+.I -lhashsum
+.IR "-lkeccak" .
+
+.SH DESCRIPTION
+The
+.B libhashsum_init_shake128_hasher
+function initialises
+.I *hasher
+for hashing using the cryptographic hash function
+SHAKE128 (a version of SHAKE), and stores hash
+function information and hashing functions for
+SHAKE128 in
+.IR *hasher .
+.PP
+.I hashbits
+shall the hash size in bits or 0, for the default
+hash size (128 bits).
+.PP
+.I hasher->algorithm
+will be set to
+.IR LIBHASHSUM_SHAKE128 .
+.PP
+.I hasher->algorithm_string
+will be set to
+.RB \(dq SHAKE128 \(dq,
+or (if
+.I hashbits
+is neither 0 nor 128)
+.RB \(dq SHAKE128[n= \fIhashbits\fP ] \(dq,
+in which case
+.I hasher->algorithm_string
+will point to a buffer in
+.IR hasher->state .
+.PP
+.I hasher->input_block_size
+will be set to the block size SHAKE128 uses, in bytes.
+.PP
+.I hasher->hash_size
+will be set to the size of SHAKE128 hashes, in bytes
+.RI ( LIBHASHSUM_SHAKE128_HASH_SIZE
+if
+.I hashbits
+is 0 or 128).
+.PP
+.I hasher->hash_output
+will be set to
+.IR NULL .
+.PP
+.I hasher->supports_non_whole_bytes
+will be set to 1
+to indicate that the
+.I *hasher->finalise
+and
+.I *hasher->finalise_const
+functions support non-zero values in their
+.I extra_bits
+parameter.
+.PP
+.I hasher->process
+will be set to a pointer to the function to call
+to feed, and process, data into the hash function.
+Its parameter
+.I this
+shall be set to
+.IR hasher .
+Its parameter
+.I data
+parameter shall be set to the buffer of data to
+process, and its parameter
+.I bytes
+shall set to the number of bytes to process from
+.IR data .
+.I *hasher->process
+will return the number of bytes processed, which
+will be a multiple of
+.IR hasher->input_block_size
+no greater than
+.IR bytes .
+.PP
+.I hasher->finalise_const
+will be set to a pointer to the function to call
+once the entire text being hashed has been loaded,
+and to get the hash of the text. It's parameter
+.I this
+shall be set to
+.IR hasher .
+Its parameter
+.I data
+shall be set to the beginning of any yet unprocessed
+data, and its parameter
+.I bytes
+shall be set to the number of bytes to process from
+.IR data .
+Its parameter
+.I extra_bits
+shall be set to the number of bits to process from
+the lower bits of the incomplete byte
+.IR data[bytes] .
+The
+.I *hasher->finalise_const
+function will return 0 upon successful completion,
+and set
+.I hasher->hash_output
+to a pointer to a buffer in
+.I hasher->state
+containing the binary hash of the processed data.
+Otherwise, the function will return -1, and set
+.I errno
+to indicate the error. The function will failure
+if:
+.RS
+.TP
+.B EINVAL
+.I extra_bits
+is 8 or greater.
+.RE
+.PP
+.I hasher->finalise
+will be set to the pointer to a function that
+is an alternative to
+.I *hasher->finalise_const
+that can support zero-copy provided that the
+buffer input as the argument
+.I data
+is sufficiently large. The
+.I *hasher->finalise
+function may rewrite
+.I data
+and shall is does not safe to use for multiple
+hashers (if the same text is hashed using multiple
+hashers,
+.I *hasher->finalise_const
+must be used). The
+function's parameter
+.I size
+shall be set to the size of the buffer
+.IR data .
+.I *hasher->finalise
+is otherwise identical to
+.IR *hasher->finalise_const .
+.PP
+.I hasher->destroy
+will be set to a pointer to a function to to
+call, with
+.I hasher
+as the argument, deallocate dynamically
+allocated data, which may invalidate any
+pointer in
+.IR *hasher .
+.PP
+.I hasher->state
+will be initialised, it shall be treated as
+internal to the library's implementation, and
+may change between versions.
+.PP
+.I hasher
+must not be
+.IR NULL .
+
+.SH RETURN VALUE
+Upon successful completion, the
+.B libhashsum_init_shake128_hasher
+function returns 0. Otherwise,
+the function returns -1 and sets
+.I errno
+to indicate the error. If -1
+is returned, the state of
+.I *hasher
+is undefined.
+
+.SH ERRORS
+The
+.B libhashsum_init_shake128_hasher
+function fails if:
+.TP
+.B ENOSYS
+Support was excluded at compile time.
+.TP
+.B ENOMEM
+Insufficient memory available.
+.TP
+.B EINVAL
+.I hashbits
+is too large.
+
+.SH HISTORY
+libhashsum 1.0.
+
+.SH SEE ALSO
+.BR libhashsum (7),
+.BR libhashsum_init_shake_hasher (3)