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104 lines
2.8 KiB
104 lines
2.8 KiB
/*
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* Minimalist Object Storage, (C) 2014 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package erasure
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// #cgo CFLAGS: -O0
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// #include <stdlib.h>
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// #include "ec-code.h"
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// #include "ec-common.h"
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import "C"
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import (
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"errors"
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"fmt"
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"unsafe"
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)
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// Decode decodes 2 tuple data containing (k + m) chunks back into its original form.
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// Additionally original block length should also be provided as input.
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//
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// Decoded data is exactly similar in length and content as the original data.
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func (e *Encoder) Decode(chunks [][]byte, length int) ([]byte, error) {
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var decode_matrix *C.uint8_t
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var decode_tbls *C.uint8_t
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var decode_index *C.uint32_t
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var source, target **C.uint8_t
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k := e.parms.K
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m := e.parms.M
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n := k + m
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if len(chunks) != int(n) {
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return nil, errors.New(fmt.Sprintf("chunks length must be %d", n))
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}
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chunk_size := GetEncodedChunkLen(length, uint8(k))
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error_index := make([]int, n+1)
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var err_count int = 0
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for i := range chunks {
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// Check of chunks are really null
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if chunks[i] == nil || len(chunks[i]) == 0 {
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error_index[err_count] = i
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err_count++
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}
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}
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error_index[err_count] = -1
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err_count++
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// Too many missing chunks, cannot be more than parity `m`
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if err_count-1 > int(n-k) {
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return nil, errors.New("too many erasures requested, can't decode")
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}
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error_index_ptr := int2cInt(error_index[:err_count])
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for i := range chunks {
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if chunks[i] == nil || len(chunks[i]) == 0 {
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chunks[i] = make([]byte, chunk_size)
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}
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}
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C.minio_init_decoder(error_index_ptr, C.int(k), C.int(n), C.int(err_count-1),
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e.encode_matrix, &decode_matrix, &decode_tbls, &decode_index)
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pointers := make([]*byte, n)
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for i := range chunks {
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pointers[i] = &chunks[i][0]
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}
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data := (**C.uint8_t)(unsafe.Pointer(&pointers[0]))
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ret := C.minio_get_source_target(C.int(err_count-1), C.int(k), C.int(m), error_index_ptr,
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decode_index, data, &source, &target)
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if int(ret) == -1 {
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return nil, errors.New("Decoding source target failed")
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}
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C.ec_encode_data(C.int(chunk_size), C.int(k), C.int(err_count-1), decode_tbls,
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source, target)
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recovered_output := make([]byte, 0, chunk_size*int(k))
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for i := 0; i < int(k); i++ {
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recovered_output = append(recovered_output, chunks[i]...)
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}
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// TODO cache this if necessary
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e.decode_matrix = decode_matrix
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e.decode_tbls = decode_tbls
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return recovered_output[:length], nil
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}
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