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# Support for str_storage: i.e., reading primitive types out of RPython string
#
# There are various possible ways to implement it, however not all of them are
# easily supported by the JIT:
#
# 1. use _get_raw_str_buf and cast the chars buffer to RAW_STORAGE_PTR: this
# works well without the JIT, but the cast to RAW_STORAGE_PTR needs to
# happen inside a short "no GC" section (like the one in
# rstr.py:copy_string_contents), which has no chance to work during
# tracing
#
# 2. cast rpy_string to a GcStruct which has the very
# same layout, with the only difference that its 'chars' field is no
# longer an Array(Char) but e.e. an Array(Signed). Then, we just need to
# read the appropriate index into the array. To support this solution,
# the JIT's optimizer needed a few workarounds. This was removed.
#
# 3. use the newly introduced 'llop.gc_load_indexed'.
#
from rpython.rtyper.lltypesystem import lltype, llmemory
from rpython.rtyper.lltypesystem.lloperation import llop
from rpython.rtyper.lltypesystem.rstr import STR
from rpython.rtyper.annlowlevel import llstr
from rpython.rlib.objectmodel import specialize
@specialize.ll()
def str_storage_getitem(TP, s, byte_offset):
# WARNING: the 'byte_offset' is, as its name says, measured in bytes;
# however, it should be aligned for TP, otherwise on some platforms this
# code will crash!
lls = llstr(s)
base_ofs = (llmemory.offsetof(STR, 'chars') +
llmemory.itemoffsetof(STR.chars, 0))
scale_factor = llmemory.sizeof(lltype.Char)
return llop.gc_load_indexed(TP, lls, byte_offset,
scale_factor, base_ofs)
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