Man page 9 : bprintf

bprintf - Parse a format string and place argsAq binary value in a buffer

int bprintf(u32 *  bin_buf , size_t  size , const char *  fmt , ... );

bin_buf
    The buffer to place argsAq binary value

size
    The size of the buffer(by words(32bits), not characters)

fmt
    The format string to use @...: Arguments for the format string

...
    variable arguments

The function returns the number of words(u32) written into bin_buf.