Add FLOAT_ZERO_HEX database function and tests

packages/sqlite-web-core/src/database_functions/float_zero_hex.rs

@@ -0,0 +1,32 @@
+use super::*;
+
+pub(crate) fn sqlite_transient() -> Option<unsafe extern "C" fn(*mut std::ffi::c_void)> {
+    // SQLite uses the value -1 cast to a function pointer as a sentinel meaning
+    // "make your own copy" for the result buffer (a.k.a. SQLITE_TRANSIENT).
+    Some(unsafe {
+        std::mem::transmute::<isize, unsafe extern "C" fn(*mut std::ffi::c_void)>(-1isize)
+    })
+}
+
+/// Scalar SQLite function that returns the canonical zero Float as a hex string.
+pub(crate) unsafe extern "C" fn float_zero_hex(
+    context: *mut sqlite3_context,
+    argc: c_int,
+    _argv: *mut *mut sqlite3_value,
+) {
+    if argc != 0 {
+        sqlite3_result_error(
+            context,
+            c"FLOAT_ZERO_HEX() does not take any arguments".as_ptr(),
+            -1,
+        );
+        sqlite3_result_error_code(context, SQLITE_MISUSE);
+        return;
+    }
+
+    let zero_hex = Float::default().as_hex();
+    let zero_hex_ptr = zero_hex.as_ptr() as *const c_char;
+    let zero_hex_len = zero_hex.len() as c_int;
+
+    sqlite3_result_text(context, zero_hex_ptr, zero_hex_len, sqlite_transient());
+}

packages/sqlite-web-core/src/database_functions/mod.rs

@@ -10,11 +10,13 @@ use std::str::FromStr;
 mod bigint_sum;
 mod float_negate;
 mod float_sum;
+mod float_zero_hex;
 mod rain_math;
 
 use bigint_sum::*;
 use float_negate::*;
 use float_sum::*;
+use float_zero_hex::*;
 
 pub use rain_math::*;
 
@@ -80,6 +82,26 @@ pub fn register_custom_functions(db: *mut sqlite3) -> Result<(), String> {
         return Err("Failed to register FLOAT_SUM function".to_string());
     }
 
+    // Register FLOAT_ZERO_HEX scalar function
+    let float_zero_hex_name = CString::new("FLOAT_ZERO_HEX").unwrap();
+    let ret = unsafe {
+        sqlite3_create_function_v2(
+            db,
+            float_zero_hex_name.as_ptr(),
+            0, // 0 arguments
+            SQLITE_UTF8 | SQLITE_DETERMINISTIC | SQLITE_INNOCUOUS,
+            std::ptr::null_mut(),
+            Some(float_zero_hex), // Scalar function
+            None,
+            None,
+            None,
+        )
+    };
+
+    if ret != SQLITE_OK {
+        return Err("Failed to register FLOAT_ZERO_HEX function".to_string());
+    }
+
     // Register FLOAT_NEGATE scalar function
     let float_negate_name = CString::new("FLOAT_NEGATE").unwrap();
     let ret = unsafe {

pkg/package.json

@@ -12,4 +12,4 @@
   "sideEffects": [
     "./snippets/*"
   ]
-}
+}