Runtime Library

Runtime Library

runtime/scratch_runtime.h is a self-contained C header included by all generated code. It detects __KERNEL__ at compile time and provides appropriate implementations for both userspace and kernel space.

Buffer pool

String-returning functions (scratch_join, scratch_ltoa, scratch_letter_of) need somewhere to put the result. We use a rotating pool of 8 static buffers:

#define SCRATCH_BUF_SIZE  1024
#define SCRATCH_BUF_COUNT 8

static char _scratch_bufs[SCRATCH_BUF_COUNT][SCRATCH_BUF_SIZE];
static int _scratch_buf_idx = 0;

Each call to a string-returning function takes the next buffer in the pool. This makes nested calls safe — scratch_join(scratch_join("a", "b"), "c") uses buffer 0 for the inner call and buffer 1 for the outer, so they don't clobber each other.

Ownership: the caller does NOT own the returned pointer. The buffer is overwritten on the next call cycle. To keep a result, copy it:

// Generated code does this for STRING variable assignment:
snprintf(my_var, sizeof(my_var), "%s", scratch_join("hello ", "world"));

Function reference

scratch_join(a, b)

Concatenates two strings. NULL-safe (NULL → "").

const char *scratch_join(const char *a, const char *b);
// scratch_join("hello ", "world") → "hello world"

scratch_ltoa(n)

Converts a long to its string representation.

const char *scratch_ltoa(long n);
// scratch_ltoa(42) → "42"

scratch_strlen(s)

Returns string length. NULL-safe (NULL → 0).

long scratch_strlen(const char *s);
// scratch_strlen("hello") → 5

scratch_letter_of(index, s)

Returns the character at position index as a 1-character string. Scratch uses 1-based indexing. Out of bounds returns "".

const char *scratch_letter_of(long index, const char *s);
// scratch_letter_of(1, "hello") → "h"
// scratch_letter_of(0, "hello") → ""

Note: uses a separate static buffer (not the pool) since it's always 2 bytes.

scratch_contains(haystack, needle)

Case-insensitive substring check. Returns 1 if found, 0 otherwise. Empty needle returns 1 (Scratch behavior).

long scratch_contains(const char *haystack, const char *needle);
// scratch_contains("Apple", "app") → 1
// scratch_contains("Apple", "z")   → 0

Kernel compatibility

When __KERNEL__ is defined:

• <linux/kernel.h> and <linux/string.h> replace <stdio.h>, <stdlib.h>, <string.h>
• atol() is provided as scratch_atol() since the kernel doesn't have the standard library version
• snprintf comes from <linux/kernel.h>

Adding a new runtime function

1. Add the implementation to scratch_runtime.h
2. Use static inline and the buffer pool if it returns a string
3. Handle NULL inputs gracefully
4. Make it work under both __KERNEL__ and userspace — avoid stdlib functions that don't exist in the kernel