13. Library interface¶
13.1. Introduction¶
.intro: This document is the design of the MPS Library Interface, a part of the plinth.
.readership: Any MPS developer. Any clients that are prepared to read this in order to get documentation.
13.2. Goals¶
.goal: The goals of the MPS library interface are:
.goal.host: To control the dependency of the MPS on the hosted ISO C library so that the core MPS remains freestanding (see design.mps.exec-env).
.goal.free: To allow the core MPS convenient access to ISO C functionality that is provided on freestanding platforms (see design.mps.exec-env.std.com.free).
13.3. Description¶
13.3.1. Overview¶
.overview.access: The core MPS needs to access functionality that could be provided by an ISO C hosted environment.
.overview.hosted: The core MPS must not make direct use of any facilities in the hosted environment (design.mps.exec-env). However, it is sensible to make use of them when the MPS is deployed in a hosted environment.
.overview.hosted.indirect: The core MPS does not make any direct use of hosted ISO C library facilities. Instead, it indirects through the MPS Library Interface, impl.h.mpslib.
.overview.free: The core MPS can make direct use of freestanding
ISO C library facilities and does not need to include any of the
header files <limits.h>, <stdarg.h>, and <stddef.h>
directly.
.overview.complete: The MPS Library Interface can be considered as the complete “interface to ISO” (in that it provides direct access to facilities that we get in a freestanding environment and equivalents of any functionality we require from the hosted environment).
.overview.provision.client: In a freestanding environment the client is expected to provide functions meeting this interface to the MPS.
.overview.provision.hosted: In a hosted environment, impl.c.mpsliban may be used. It just maps impl.h.mpslib directly onto the ISO C library equivalents.
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13.3.2. Outside the interface¶
We provide impl.c.mpsliban to the client, for two reasons:
the client can use it to connect the MPS to the ISO C library if it exists;
as an example implementation of the MPS Library Interface.
13.4. Implementation¶
.impl: The MPS Library Interface comprises a header file impl.h.mpslib and some documentation.
.impl.decl: The header file defines the interface to definitions which parallel those parts of the non-freestanding ISO headers which are used by the MPS.
.impl.include: The header file also includes the freestanding
headers <limits.h>, <stdarg.h>, and <stddef.h> (and not
<float.h>, though perhaps it should).
