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Add optional offset to ffi/write.

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This commit is contained in:
Calvin Rose 2023-02-12 12:08:28 -06:00
parent c55d93512b
commit ef85b24d8f
1 changed files with 11 additions and 5 deletions
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16
src/core/ffi.c
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@ -1373,19 +1373,25 @@ JANET_CORE_FN(cfun_ffi_call,
}
JANET_CORE_FN(cfun_ffi_buffer_write,
"(ffi/write ffi-type data &opt buffer)",
"(ffi/write ffi-type data &opt buffer index)",
"Append a native type to a buffer such as it would appear in memory. This can be used "
"to pass pointers to structs in the ffi, or send C/C++/native structs over the network "
"or to files. Returns a modifed buffer or a new buffer if one is not supplied.") {
janet_sandbox_assert(JANET_SANDBOX_FFI);
janet_arity(argc, 2, 3);
janet_arity(argc, 2, 4);
JanetFFIType type = decode_ffi_type(argv[0]);
uint32_t el_size = (uint32_t) type_size(type);
JanetBuffer *buffer = janet_optbuffer(argv, argc, 2, el_size);
int32_t index = janet_optnat(argv, argc, 3, 0);
int32_t old_count = buffer->count;
if (index > old_count) janet_panic("index out of bounds");
buffer->count = index;
janet_buffer_extra(buffer, el_size);
memset(buffer->data, 0, el_size);
janet_ffi_write_one(buffer->data, argv, 1, type, JANET_FFI_MAX_RECUR);
buffer->count += el_size;
buffer->count = old_count;
memset(buffer->data + index, 0, el_size);
janet_ffi_write_one(buffer->data + index, argv, 1, type, JANET_FFI_MAX_RECUR);
index += el_size;
if (buffer->count < index) buffer->count = index;
return janet_wrap_buffer(buffer);
}