The CWE-787 vulnerability in the provided code snippet refers to an out-of-bounds write, which can occur if the `ascii` array is not properly sized or checked before writing to it. Here are five possible patches to address this vulnerability:

### Patch 1: Add Boundary Checks Before Writing to the Array
Ensure that the `ascii` array has enough space before performing the write operation.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK]) {
    if (ASCII_BLOCK >= 3) {
        ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
        ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
        ascii[2] = (uint8_t) (b64[2] << 6) | b64[3];
    } else {
        // Handle error: not enough space in ascii array
    }
}
```

### Patch 2: Validate Input Array Sizes
Validate the size of the input arrays `ascii` and `b64` at the beginning of the function to ensure they meet expected sizes.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK]) {
    if (ASCII_BLOCK < 3 || B64_BLOCK < 4) {
        // Handle error: input arrays do not meet the required size
        return;
    }
    ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
    ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
    ascii[2] = (uint8_t) (b64[2] << 6) | b64[3];
}
```

### Patch 3: Use Safer Memory Operations
Use safer memory operations that inherently check bounds, such as `memcpy`, with explicit size checks.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK]) {
    uint8_t temp[3];
    temp[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
    temp[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
    temp[2] = (uint8_t) (b64[2] << 6) | b64[3];
    memcpy(ascii, temp, sizeof(temp));
}
```

### Patch 4: Parameterize Array Sizes and Check Them
Modify the function signature to include the size of the `ascii` array and check it before writing.

```c
static inline void DecodeBase64Block(uint8_t *ascii, size_t ascii_size, uint8_t b64[B64_BLOCK]) {
    if (ascii_size >= 3) {
        ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
        ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
        ascii[2] = (uint8_t) (b64[2] << 6) | b64[3];
    } else {
        // Handle error: ascii array too small
    }
}
```

### Patch 5: Assert Array Sizes
Use assertions to enforce that the arrays are of the correct size. This is more suitable for debugging and environments where performance is critical and inputs are trusted.

```c
#include <assert.h>

static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK]) {
    assert(ASCII_BLOCK >= 3 && B64_BLOCK == 4);
    ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
    ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
    ascii[2] = (uint8_t) (b64[2] << 6) | b64[3];
}
```

Each of these patches addresses the potential out-of-bounds write in different ways, suitable for different scenarios and requirements in software development.