implement it - easier than expected

wasm-module/src/ratio.rs

@@ -41,8 +41,17 @@ pub fn ratio_from_float(value:f64)->Result<Ratio64,RatioFromFloatError>{
 	// value = sign * mantissa * 2 ^ exponent
 	let (mantissa, exponent, sign) = f64_into_parts(value);
 
+	if 0<=exponent{
+		// we know value < i64::MIN, so it must just be an integer.
+		return Ok(Ratio64::new((sign as i64*mantissa as i64)<<exponent,1).unwrap());
+	}
+
+	if exponent< -62{
+		// very small number is not representable
+		return Ok(Ratio64::ZERO);
+	}
+
 	// the idea: create exact float num/den ratio, and compute continued fraction if it doesn't fit
-
-
-	return Ok(())
+	// oh actually we can just straight up represent all floats exactly. ok.
+	Ok(Ratio64::new(sign as i64*mantissa as i64, 1<<-exponent).unwrap())
 }