Merge pull request #1852 from mjf/space-lua-add-frexp-and-ldexp

[Space Lua] Add `math.frexp` and `math.ldexp` and tests

client/space_lua/stdlib/math.ts

@@ -118,6 +118,33 @@ export const mathApi = new LuaTable({
     return new LuaMultiRes([int, frac]);
   }),
 
+  // Returns m and e such that x = m * 2^e, 0.5 <= |m| < 1 (or m=0 when x=0).
+  // e is an integer. Mirrors C99/Lua.
+  // Special cases: frexp(0) = (0, 0); frexp(+-inf/nan) = (x, 0).
+  frexp: new LuaBuiltinFunction((_sf, x: number) => {
+    const xn = untagNumber(x);
+    if (xn === 0 || !isFinite(xn) || isNaN(xn)) {
+      return new LuaMultiRes([xn, 0]);
+    }
+    const abs = Math.abs(xn);
+    let e = Math.floor(Math.log2(abs)) + 1;
+    let m = xn / Math.pow(2, e);
+    if (Math.abs(m) >= 1.0) {
+      e += 1;
+      m /= 2;
+    }
+    if (Math.abs(m) < 0.5) {
+      e -= 1;
+      m *= 2;
+    }
+    return new LuaMultiRes([m, e]);
+  }),
+
+  // Returns m * 2^e (the inverse of frexp).  Mirrors C99/Lua.
+  ldexp: new LuaBuiltinFunction((_sf, m: number, e: number) =>
+    untagNumber(m) * Math.pow(2, untagNumber(e))
+  ),
+
   // Power and logarithms
   exp: new LuaBuiltinFunction((_sf, x: number) => Math.exp(untagNumber(x))),
   log: new LuaBuiltinFunction((_sf, x: number, base?: number) => {
@@ -126,6 +153,7 @@ export const mathApi = new LuaTable({
     }
     return Math.log(untagNumber(x)) / Math.log(untagNumber(base));
   }),
+  // Power function (deprecated in Lua 5.4 but retained for compatibility)
   pow: new LuaBuiltinFunction((_sf, x: number, y: number) =>
     Math.pow(untagNumber(x), untagNumber(y))
   ),
@@ -144,7 +172,7 @@ export const mathApi = new LuaTable({
     return Math.atan2(untagNumber(y), untagNumber(x));
   }),
 
-  // Hyperbolic functions
+  // Hyperbolic functions (deprecated in Lua 5.4 but retained for compatibility)
   cosh: new LuaBuiltinFunction((_sf, x: number) => Math.cosh(untagNumber(x))),
   sinh: new LuaBuiltinFunction((_sf, x: number) => Math.sinh(untagNumber(x))),
   tanh: new LuaBuiltinFunction((_sf, x: number) => Math.tanh(untagNumber(x))),

client/space_lua/stdlib/math_test.lua

@@ -317,3 +317,34 @@ do
   local j2 = math.random()
   assertEquals(j1, j2, "determinism restored after re-seed")
 end
+
+-- frexp / ldexp
+do
+  -- frexp: x = m * 2^e, 0.5 <= |m| < 1
+  local m, e = math.frexp(8)
+  assertClose(m, 0.5, 1e-15, "frexp(8) m")
+  assertEquals(e, 4, "frexp(8) e")
+
+  local m2, e2 = math.frexp(1)
+  assertClose(m2, 0.5, 1e-15, "frexp(1) m")
+  assertEquals(e2, 1, "frexp(1) e")
+
+  local m3, e3 = math.frexp(-4)
+  assertClose(m3, -0.5, 1e-15, "frexp(-4) m")
+  assertEquals(e3, 3, "frexp(-4) e")
+
+  local m4, e4 = math.frexp(0)
+  assertEquals(m4, 0, "frexp(0) m")
+  assertEquals(e4, 0, "frexp(0) e")
+
+  -- ldexp: m * 2^e
+  assertClose(math.ldexp(0.5, 4), 8.0, 1e-15, "ldexp(0.5,4)")
+  assertClose(math.ldexp(0.5, 1), 1.0, 1e-15, "ldexp(0.5,1)")
+  assertClose(math.ldexp(-0.5, 3), -4.0, 1e-15, "ldexp(-0.5,3)")
+  assertClose(math.ldexp(0.0, 10), 0.0, 1e-15, "ldexp(0,10)")
+
+  -- round-trip: ldexp(frexp(x)) == x
+  local orig = 3.14159
+  local fm, fe = math.frexp(orig)
+  assertClose(math.ldexp(fm, fe), orig, 1e-14, "frexp/ldexp round-trip")
+end