[Mesa-dev] [wip 1/9] glsl: memory_writer helper class for data serialization

[Paul Berry]

On 14 January 2014 02:35, Tapani Pälli <tapani.palli at intel.com> wrote:

>  On 01/13/2014 08:27 PM, Paul Berry wrote:
>
> On 2 January 2014 03:58, Tapani Pälli <tapani.palli at intel.com> wrote:
>
>> Class will be used by the shader binary cache implementation.
>>
>> Signed-off-by: Tapani Pälli <tapani.palli at intel.com>
>> ---
>>  src/glsl/memory_writer.h | 147
>> +++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 147 insertions(+)
>>  create mode 100644 src/glsl/memory_writer.h
>>
>> diff --git a/src/glsl/memory_writer.h b/src/glsl/memory_writer.h
>> new file mode 100644
>> index 0000000..a6c6b55
>> --- /dev/null
>> +++ b/src/glsl/memory_writer.h
>> @@ -0,0 +1,147 @@
>> +/* -*- c++ -*- */
>> +/*
>> + * Copyright © 2013 Intel Corporation
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining
>> a
>> + * copy of this software and associated documentation files (the
>> "Software"),
>> + * to deal in the Software without restriction, including without
>> limitation
>> + * the rights to use, copy, modify, merge, publish, distribute,
>> sublicense,
>> + * and/or sell copies of the Software, and to permit persons to whom the
>> + * Software is furnished to do so, subject to the following conditions:
>> + *
>> + * The above copyright notice and this permission notice (including the
>> next
>> + * paragraph) shall be included in all copies or substantial portions of
>> the
>> + * Software.
>> + *
>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
>> EXPRESS OR
>> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
>> MERCHANTABILITY,
>> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT
>> SHALL
>> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
>> OTHER
>> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
>> ARISING
>> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>> + * DEALINGS IN THE SOFTWARE.
>> + */
>> +
>> +#pragma once
>> +#ifndef MEMORY_WRITER_H
>> +#define MEMORY_WRITER_H
>> +
>> +#include <stdlib.h>
>> +#include <unistd.h>
>> +#include <string.h>
>> +
>> +#ifdef __cplusplus
>> +/**
>> + * Helper class for writing data to memory
>> + *
>> + * This class maintains a dynamically-sized memory buffer and allows
>> + * for data to be efficiently appended to it with automatic resizing.
>> + */
>> +class memory_writer
>> +{
>> +public:
>> +   memory_writer() :
>> +      memory(NULL),
>> +      curr_size(0),
>> +      pos(0) {}
>> +
>> +   ~memory_writer()
>> +   {
>> +      free(memory);
>> +   }
>> +
>> +   /* user wants to claim the memory */
>> +   char *release_memory(size_t *size)
>> +   {
>> +      /* final realloc to free allocated but unused memory */
>> +      char *result = (char *) realloc(memory, pos);
>> +      *size = pos;
>> +      memory = NULL;
>> +      curr_size = 0;
>> +      pos = 0;
>> +      return result;
>> +   }
>> +
>> +/**
>> + * write functions per type
>> + */
>> +#define DECL_WRITER(type) int write_ ##type (const type data) {\
>> +   return write(&data, sizeof(type));\
>> +}
>> +
>> +   DECL_WRITER(int32_t);
>> +   DECL_WRITER(int64_t);
>> +   DECL_WRITER(uint8_t);
>> +   DECL_WRITER(uint32_t);
>> +
>> +   int write_bool(bool data)
>> +   {
>> +      uint8_t val = data;
>> +      return write_uint8_t(val);
>> +   }
>> +
>> +   /* write function that reallocates more memory if required */
>> +   int write(const void *data, int32_t size)
>> +   {
>> +      if (!memory || pos > (int32_t)(curr_size - size))
>> +         if (grow(size))
>> +            return -1;
>> +
>> +      memcpy(memory + pos, data, size);
>> +
>> +      pos += size;
>> +      return 0;
>> +   }
>> +
>> +   int overwrite(const void *data, int32_t size, int32_t offset)
>> +   {
>> +      if (offset < 0 || offset + size > pos)
>> +         return -1;
>> +      memcpy(memory + offset, data, size);
>> +      return 0;
>> +   }
>> +
>> +   int write_string(const char *str)
>> +   {
>> +      if (!str)
>> +         return -1;
>> +      char terminator = '\0';
>> +      write(str, strlen(str));
>> +      write(&terminator, 1);
>>
>
>  C strings include a terminator, so there's no reason to write out the
> string contents and the terminator separtely.  You can just do:
>
>  write(str, strlen(str) + 1);
>
> Also, don't forget to propagate the return code to the caller:
>
>  return write(str, strlen(str) + 1);
>
>
> Ah right, will do. It could be that this needs to be modified back to how
> it was though (to write to length of the string too). I think it is
> otherwise impossible for the reader side to know if terminator really
> exists and it might continue to read forever (or call strlen for
> unterminated string).
>

I don't know of any C library function that does exactly what you want.  Of
course you could always code up your own loop.  But I think I agree that
storing the length first is the best approach.
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