My intention was to analyze, how C-pointer-arithmetic are translated to WASM code. Assuming you have got the a  C++ file foo.cpp like:

/// @file foo.cpp
#include <emscripten.h> // macro EMSCRIPTEN_KEEPALIVE
#include <stdint.h>

extern "C" {
void EMSCRIPTEN_KEEPALIVE myfunction(uint8_t *dst, uint8_t *src) {
 dst[0] = src[0];
 dst[1] = src[1];
}
} // extern "C"

The following code will produce  the output file foo.wasm wiht the the corresponding WASM code (file size arond 255 bytes):

emcc foo.cpp -v -O3 -s ONLY_MY_CODE=1 -s WASM=1 -s SIDE_MODULE=1 -o foo.wasm

Check the content of this file using the disassembler tool wasm-dis form project binaryen:

wasm-dis foo.wasm

The output of the disassembler looks like:

(module
 (type $0 (func (param i32 i32)))
 (type $1 (func))
 (import "env" "memoryBase" (global $import$0 i32))
 (import "env" "memory" (memory $0 256))
 (import "env" "table" (table 0 anyfunc))
 (import "env" "tableBase" (global $import$3 i32))
 (global $global$0 (mut i32) (i32.const 0))
 (global $global$1 (mut i32) (i32.const 0))
 (export "_myfunction" (func $0))
 (export "__post_instantiate" (func $2))
 (export "runPostSets" (func $1))
 (func $0 (type $0) (param $var$0 i32) (param $var$1 i32)
 (block $label$0
 (i32.store8
 (get_local $var$0)
 (i32.load8_s
 (get_local $var$1)
 )
 )
 (i32.store8 offset=1
 (get_local $var$0)
 (i32.load8_s offset=1
 (get_local $var$1)
 )
 )
 )
 )
 (func $1 (type $1)
 (nop)
 )
 (func $2 (type $1)
 (block $label$0
 (set_global $global$0
 (get_global $import$0)
 )
 (set_global $global$1
 (i32.add
 (get_global $global$0)
 (i32.const 5242880)
 )
 )
 (call $1)
 )
 )
 ;; custom section "dylink", size 5
)

The disassembled code shows, that no dependencies to JS or other runtimes exists. Still a number of functions can be identified in the  import and export section,  “myfunction” does not depend on actually.

Note: Just in case, please let me know how to eliminate the imports of “memoryBase”, “memory”, “table”, “tableBase”, and eliminating the exports of  “__post_instantiate”, “runPostSets”.

The following code shows the disassembled operations of ‘myfunction’ (function $0).  AFAICS, the pointer parameters are of type i32, and the index is translated to a bytewise store8/load8 using the offset feature, for example ‘offset=1’.

(func $0 (type $0) (param $var$0 i32) (param $var$1 i32)
 (block $label$0
 (i32.store8
 (get_local $var$0)
 (i32.load8_s
 (get_local $var$1)
 )
 )
 (i32.store8 offset=1
 (get_local $var$0)
 (i32.load8_s offset=1
 (get_local $var$1)
 )
 )
 )
 )