iscntrl() in bionic (Android's libc)

iscntrl_test.c

#include <stdio.h>
#include <string.h>
#include <android/log.h>

#define LOGV(...)  __android_log_print(ANDROID_LOG_VERBOSE,LOG_TAG,__VA_ARGS__)

void test(void) {
  char log_line[256];
  char buff[8];
  int i = 0;
  while (i < 0x100) {
    memset((void *)log_line, 0, 256);
    char *ptr = log_line;
    sprintf(buff, "0x%02x | ", i);
    strcpy(ptr, buff);
    ptr = log_line + strlen(log_line);
    
    for (int j = 0; j < 8; ++j) {
	sprintf(buff, "%02d ", iscntrl(i));
	++i;

	strcpy(ptr, buff);
	ptr = log_line + strlen(log_line);
    }

    LOGV(log_line);
  }
}

log.txt

0x00 | 32 32 32 32 32 32 32 32
0x08 | 32 32 32 32 32 32 32 32
0x10 | 32 32 32 32 32 32 32 32
0x18 | 32 32 32 32 32 32 32 32
0x20 | 00 00 00 00 00 00 00 00
0x28 | 00 00 00 00 00 00 00 00
0x30 | 00 00 00 00 00 00 00 00
0x38 | 00 00 00 00 00 00 00 00
0x40 | 00 00 00 00 00 00 00 00
0x48 | 00 00 00 00 00 00 00 00
0x50 | 00 00 00 00 00 00 00 00
0x58 | 00 00 00 00 00 00 00 00
0x60 | 00 00 00 00 00 00 00 00
0x68 | 00 00 00 00 00 00 00 00
0x70 | 00 00 00 00 00 00 00 00
0x78 | 00 00 00 00 00 00 00 32
0x80 | 32 32 32 32 32 32 32 32
0x88 | 32 32 32 32 32 32 32 32
0x90 | 32 32 32 32 32 32 32 32
0x98 | 32 32 32 32 32 32 32 32
0xa0 | 00 00 00 00 00 00 00 00
0xa8 | 00 00 00 00 00 00 00 00
0xb0 | 00 00 00 00 00 00 00 00
0xb8 | 00 00 00 00 00 00 00 00
0xc0 | 00 00 00 00 00 00 00 00
0xc8 | 00 00 00 00 00 00 00 00
0xd0 | 00 00 00 00 00 00 00 00
0xd8 | 00 00 00 00 00 00 00 00
0xe0 | 00 00 00 00 00 00 00 00
0xe8 | 00 00 00 00 00 00 00 00
0xf0 | 00 00 00 00 00 00 00 00
0xf8 | 00 00 00 00 00 00 00 00