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

[Ian Romanick]

On 01/02/2014 03:58 AM, Tapani Pälli 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)

I agree with Paul's previous comments about the return values.

http://lists.freedesktop.org/archives/mesa-dev/2013-November/047740.html

It looks like the only errors tested are either memory allocation or bad
parameters.  The bad parameter checks should just be assertions.

> +   {
> +      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);

This should just be

      write(str, strlen(str) + 1);

> +      return 0;
> +   }
> +
> +   inline int32_t position() { return pos; }
> +
> +
> +private:
> +
> +   /* reallocate more memory */
> +   int grow(int32_t size)
> +   {
> +      int32_t new_size = 2 * (curr_size + size);
> +      char *more_mem = (char *) realloc(memory, new_size);
> +      if (more_mem == NULL) {
> +         free(memory);
> +         memory = NULL;
> +         return -1;
> +      } else {
> +         memory = more_mem;
> +         curr_size = new_size;
> +         return 0;
> +      }
> +   }
> +
> +   /* allocated memory */
> +   char *memory;
> +
> +   /* current size of the whole allocation */
> +   int32_t curr_size;

Is there a reason to specifically make this int32_t instead of just int?
 Or even unsigned?

> +
> +   /* write position / size of the data written */
> +   int32_t pos;
> +};
> +
> +#endif /* ifdef __cplusplus */
> +
> +#endif /* MEMORY_WRITER_H */
>