Zokrates WASM version of Rust helpers

bits.c

#define WASM_EXPORT __attribute__((visibility("default")))

typedef unsigned long int uint32_t;
typedef long int int32_t;
typedef unsigned char field_t[32];

/* List of exports */
WASM_EXPORT
const int32_t field_size = sizeof(field_t);     /* Maximum accepted number of bytes to encode a field */
WASM_EXPORT
const int32_t min_inputs = 1;                    /* Expected number of inputs */
WASM_EXPORT
const int32_t min_outputs = 254;                 /* Expected number of outputs */

field_t input;                                  /* Place to store the single input */
field_t output[254];                            /* Place to recover the output from */

WASM_EXPORT
uint32_t get_inputs_off()
{
  return (uint32_t)&input;
}

void zero_out(unsigned char *field, int size)
{
  for (int i=0; i<size; i++)
    field[i] = 0;
}

WASM_EXPORT
uint32_t solve()
{
  /* Make sure that memory is zeroed-out */
  zero_out((unsigned char *) &output, 32*254);

  /* Loop over all the field's bits */
  for (int i=0; i<254; i++) {
    /* Byte index of the current bit */
    int byte = i / 8;
    /* Bit index of the current bit */
    unsigned char mask = 1 << (i % 8);

    /* Store the bit, assuming little endian */
    output[i][0] = input[byte] & mask ? 1 : 0;
  }

  return (uint32_t)&output;
}

bits_v2.c

#define WASM_EXPORT __attribute__((visibility("default")))

WASM_EXPORT
const int field_size = 32;
WASM_EXPORT
const int min_inputs = 1;
WASM_EXPORT
const int min_outputs = 254;

unsigned char input[field_size];
unsigned char output[min_outputs][field_size];

WASM_EXPORT
int get_inputs_off() {
  return (int) &input;
}

WASM_EXPORT
int solve(void) {
  for (int i=min_outputs-1; i>=0; i--) {
    output[min_outputs-i-1 /* BE */][0 /* LE */] = (input[i/8] & (1 << (i % 8))) ? 1 : 0;
  }
  return (int) &output;
}

identity.wast

(module
 (type $0 (func (result i32)))
 (global $global$0 i32 (i32.const 1))
 (global $global$1 i32 (i32.const 1))
 (global $global$2 i32 (i32.const 32))
 (global $global$3 (mut i32) (i32.const 0))
 (memory $0 1)
 (data (i32.const 0) "\ff\ff\ff\ff\00\00\00\00\00\00\00\00\00\00\00\00\ff\ff\ff\ff\00\00\00\00\00\00\00\00\00\00\00\00")
 (data (i32.const 32) "\de\ad\be\ef\00\00\00\00\00\00\00\00\00\00\00\00\de\ad\be\ef\00\00\00\00\00\00\00\00\00\00\00\00")
 (export "memory" (memory $0))
 (export "get_inputs_off" (func $1))
 (export "solve" (func $0))
 (export "min_inputs" (global $global$0))
 (export "min_outputs" (global $global$1))
 (export "field_size" (global $global$2))
 (func $0 (; 0 ;) (type $0) (result i32)
  (loop $label$1
   (i32.store
    (i32.add
     (i32.const 32)
     (get_global $global$3)
    )
    (i32.load
     (i32.add
      (i32.const 0)
      (get_global $global$3)
     )
    )
   )
   (set_global $global$3
    (i32.add
     (get_global $global$3)
     (i32.const 1)
    )
   )
   (br_if $label$1
    (i32.ne
     (get_global $global$3)
     (get_global $global$2)
    )
   )
  )
; Set loop counter back to 0 for next function call
  (set_global $global$3
   (i32.const 0)
  )
  (i32.const 32)
 )
 (func $1 (; 1 ;) (type $0) (result i32)
  (i32.const 0)
 )
)