[Mesa-dev] [PATCH 3/8] compiler/blob: Rework blob_reserve_bytes

[Connor Abbott]

I like the version I wrote a little better. The main difference is
that instead of the alignment parameter, I added a
blob_reserve_intptr() function to match blob_read_intptr() and
blob_write_intptr(). I also updated the doxygen comment for the
function, and had a little more descriptive commit message:
https://cgit.freedesktop.org/~cwabbott0/mesa/commit/?h=nir-serialize&id=f2e1e0df8d0d24afc072bcd47d86338436b3fdc2

On Fri, Sep 15, 2017 at 9:39 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
> This commit primarily makes two changes.  First, blob_reserve_bytes now
> takes an alignment parameter.  Second, we now return an offset into the
> blob instead of a pointer and leave the pointer arithmetic to the
> caller.  This way you can call blob_reserve_bytes, emit a bunch more
> stuff, and then come back and fill in the reserved data.
> ---
>  src/compiler/blob.c                 | 14 ++++++++------
>  src/compiler/blob.h                 |  8 ++++----
>  src/compiler/glsl/tests/blob_test.c |  7 ++++---
>  3 files changed, 16 insertions(+), 13 deletions(-)
>
> diff --git a/src/compiler/blob.c b/src/compiler/blob.c
> index 3c4aed8..7324a6b 100644
> --- a/src/compiler/blob.c
> +++ b/src/compiler/blob.c
> @@ -139,18 +139,20 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write)
>     return true;
>  }
>
> -uint8_t *
> -blob_reserve_bytes(struct blob *blob, size_t to_write)
> +size_t
> +blob_reserve_bytes(struct blob *blob, size_t to_write, size_t align)
>  {
> -   uint8_t *ret;
> +   size_t offset;
> +
> +   align_blob(blob, align);
>
>     if (! grow_to_fit (blob, to_write))
> -      return NULL;
> +      return (size_t)-1;
>
> -   ret = blob->data + blob->size;
> +   offset = blob->size;
>     blob->size += to_write;
>
> -   return ret;
> +   return offset;
>  }
>
>  bool
> diff --git a/src/compiler/blob.h b/src/compiler/blob.h
> index 940c81e..e1f7fe7 100644
> --- a/src/compiler/blob.h
> +++ b/src/compiler/blob.h
> @@ -113,11 +113,11 @@ blob_write_bytes(struct blob *blob, const void *bytes, size_t to_write);
>   * that is not aware of the blob API, (so that blob_write_bytes cannot be
>   * called).
>   *
> - * \return A pointer to space allocated within \blob to which \to_write bytes
> - * can be written, (or NULL in case of any allocation error).
> + * \return The offset into \blob at which \to_write bytes can be written, (or
> + * NULL in case of any allocation error).
>   */
> -uint8_t *
> -blob_reserve_bytes(struct blob *blob, size_t to_write);
> +size_t
> +blob_reserve_bytes(struct blob *blob, size_t to_write, size_t align);
>
>  /**
>   * Overwrite some data previously written to the blob.
> diff --git a/src/compiler/glsl/tests/blob_test.c b/src/compiler/glsl/tests/blob_test.c
> index df0e91a..e82ceb1 100644
> --- a/src/compiler/glsl/tests/blob_test.c
> +++ b/src/compiler/glsl/tests/blob_test.c
> @@ -120,7 +120,7 @@ test_write_and_read_functions (void)
>  {
>     struct blob *blob;
>     struct blob_reader reader;
> -   uint8_t *reserved;
> +   size_t reserved_offset;
>     size_t str_offset, uint_offset;
>     uint8_t reserve_buf[sizeof(reserve_test_str)];
>
> @@ -130,8 +130,9 @@ test_write_and_read_functions (void)
>
>     blob_write_bytes(blob, bytes_test_str, sizeof(bytes_test_str));
>
> -   reserved = blob_reserve_bytes(blob, sizeof(reserve_test_str));
> -   memcpy(reserved, reserve_test_str, sizeof(reserve_test_str));
> +   reserved_offset = blob_reserve_bytes(blob, sizeof(reserve_test_str), 1);
> +   memcpy(blob->data + reserved_offset,
> +          reserve_test_str, sizeof(reserve_test_str));
>
>     /* Write a placeholder, (to be replaced later via overwrite_bytes) */
>     str_offset = blob->size;
> --
> 2.5.0.400.gff86faf
>
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