#define NULL ((void *)0)
typedef unsigned long size_t; // Customize by platform.
typedef long intptr_t;
typedef unsigned long uintptr_t;
typedef long scalar_t__; // Either arithmetic or pointer type.
/* By default, we understand bool (as a convenience). */
typedef int bool;
#define false 0
#define true 1

/* Forward declarations */

/* Type definitions */
typedef int /*<<< orphan*/ alphanum;

/* Variables and functions */
int rand();
void gen_random(char *s, const int len) {
  static const char alphanum[] = "0123456789"
                                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                 "abcdefghijklmnopqrstuvwxyz";
  for (int i = 0; i < len; ++i) {
    s[i] = alphanum[rand() % (sizeof(alphanum) - 1)];
  }
  s[len] = 0;
}


x86 assembly (clang, -O0):
<gen_random>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
mov    %rdi,-0x8(%rbp)
mov    %esi,-0xc(%rbp)
movl   $0x0,-0x10(%rbp)
mov    -0x10(%rbp),%eax
cmp    -0xc(%rbp),%eax
jge    1168 <gen_random+0x58>
mov    $0x0,%al
call   1030 <rand@plt>
cltq
mov    $0x3e,%ecx
xor    %edx,%edx
div    %rcx
lea    0xeb4(%rip),%rax
mov    (%rax,%rdx,1),%dl
mov    -0x8(%rbp),%rax
movslq -0x10(%rbp),%rcx
mov    %dl,(%rax,%rcx,1)
mov    -0x10(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x10(%rbp)
jmp    1126 <gen_random+0x16>
mov    -0x8(%rbp),%rax
movslq -0xc(%rbp),%rcx
movb   $0x0,(%rax,%rcx,1)
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<gen_random>:
push   %rbp
push   %r15
push   %r14
push   %r13
push   %r12
push   %rbx
push   %rax
mov    %esi,%r14d
mov    %rdi,%r13
test   %esi,%esi
jle    117d <gen_random+0x6d>
mov    %r14d,%ebp
movabs $0x8421084210842109,%r15
08 21 84
lea    0xec7(%rip),%r12
xor    %ebx,%ebx
nopl   0x0(%rax,%rax,1)
xor    %eax,%eax
call   1030 <rand@plt>
movslq %eax,%rcx
mov    %rcx,%rax
shr    %rax
mul    %r15
shr    $0x4,%rdx
mov    %rdx,%rax
shl    $0x6,%rax
mov    %rdx,%rsi
sub    %rax,%rsi
add    %rdx,%rsi
add    %rcx,%rsi
movzbl (%r12,%rsi,1),%eax
mov    %al,0x0(%r13,%rbx,1)
add    $0x1,%rbx
cmp    %rbx,%rbp
jne    1140 <gen_random+0x30>
movslq %r14d,%rax
movb   $0x0,0x0(%r13,%rax,1)
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r13
pop    %r14
pop    %r15
pop    %rbp
ret

LLVM IR (-O0):
@gen_random.alphanum = internal constant [63 x i8] c"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz\00"
define void @gen_random(i8* %0, i32 %1) {
%3 = alloca i8*
%4 = alloca i32
%5 = alloca i32
store i8* %0, i8** %3
store i32 %1, i32* %4
store i32 0, i32* %5
br label %6
6: ; preds = %20, %2
%7 = load i32, i32* %5
%8 = load i32, i32* %4
%9 = icmp slt i32 %7, %8
br i1 %9, label %10, label %23
10: ; preds = %6
%11 = call i32 (...) @rand()
%12 = sext i32 %11 to i64
%13 = urem i64 %12, 62
%14 = getelementptr inbounds [63 x i8], [63 x i8]* @gen_random.alphanum, i64 0, i64 %13
%15 = load i8, i8* %14
%16 = load i8*, i8** %3
%17 = load i32, i32* %5
%18 = sext i32 %17 to i64
%19 = getelementptr inbounds i8, i8* %16, i64 %18
store i8 %15, i8* %19
br label %20
20: ; preds = %10
%21 = load i32, i32* %5
%22 = add nsw i32 %21, 1
store i32 %22, i32* %5
br label %6
23: ; preds = %6
%24 = load i8*, i8** %3
%25 = load i32, i32* %4
%26 = sext i32 %25 to i64
%27 = getelementptr inbounds i8, i8* %24, i64 %26
store i8 0, i8* %27
ret void
}

LLVM IR (-O2):
@gen_random.alphanum = internal unnamed_addr constant [63 x i8] c"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz\00"
define void @gen_random(i8* nocapture writeonly %0, i32 %1) {
%3 = icmp sgt i32 %1, 0
br i1 %3, label %4, label %6
4: ; preds = %2
%5 = zext i32 %1 to i64
br label %9
6: ; preds = %9, %2
%7 = sext i32 %1 to i64
%8 = getelementptr inbounds i8, i8* %0, i64 %7
store i8 0, i8* %8
ret void
9: ; preds = %4, %9
%10 = phi i64 [ 0, %4 ], [ %17, %9 ]
%11 = tail call i32 (...) @rand()
%12 = sext i32 %11 to i64
%13 = urem i64 %12, 62
%14 = getelementptr inbounds [63 x i8], [63 x i8]* @gen_random.alphanum, i64 0, i64 %13
%15 = load i8, i8* %14
%16 = getelementptr inbounds i8, i8* %0, i64 %10
store i8 %15, i8* %16
%17 = add nuw nsw i64 %10, 1
%18 = icmp eq i64 %17, %5
br i1 %18, label %6, label %9
}