Refactor for consistency

src/header/stdlib/lcg48.rs

@@ -2,50 +2,27 @@
 
 use platform::types::*;
 
-/* The current element of the linear congruential generator's sequence. Any
- * function that sets this variable must ensure that only the lower 48 bits get
- * set. */
-pub static mut XI: u64 = 0;
+/* The default element buffer for the linear congruential generator's
+ * sequence. Implemented using a c_ushort array for consistency between
+ * the drand48()/lrand48()/mrand48() and erand48()/nrand48()/jrand48()
+ * functions, and with STASHED_XI (see below). */
+pub static mut DEFAULT_XI: [c_ushort; 3] = [0; 3];
 
 // Used by seed48() (returns a pointer to this array).
 pub static mut STASHED_XI: [c_ushort; 3] = [0; 3];
 
-/* Multiplier and addend, which may be set through lcong48(). Default values as
- * specified in POSIX. */
-const A_DEFAULT: u64 = 0x5deece66d;
-const C_DEFAULT: u16 = 0xb;
+/* Multiplier and addend, which may be set through lcong48(). Default
+ * values as specified in POSIX. */
+const A_DEFAULT_VALUE: u64 = 0x5deece66d;
+const C_DEFAULT_VALUE: u16 = 0xb;
 
-pub static mut A: u64 = A_DEFAULT;
-pub static mut C: u16 = C_DEFAULT;
+pub static mut A: u64 = A_DEFAULT_VALUE;
+pub static mut C: u16 = C_DEFAULT_VALUE;
 
-/// Gets the next element in the linear congruential generator's
-/// sequence.
-pub unsafe fn next_x(x: u64) -> u64 {
-    /* The recurrence relation of the linear congruential generator,
-     * X_(n+1) = (a * X_n + c) % m,
-     * with m = 2**48. The multiplication and addition can overflow a u64, but
-     * we just let it wrap since we take mod 2**48 anyway. */
-    A.wrapping_mul(x).wrapping_add(u64::from(C)) & 0xffff_ffff_ffff
-}
-
-/// Get a C `double` from a 48-bit integer (for `drand48()` and `erand48()`).
-pub fn x_to_float64(x: u64) -> c_double {
-    /* We set the exponent to 0, and the 48-bit integer is copied into the high
-     * 48 of the 52 significand bits. The value then lies in the range
-     * [1.0, 2.0), from which we simply subtract 1.0. */
-    f64::from_bits(0x3ff0_0000_0000_0000_u64 | (x << 4)) - 1.0f64
-}
-
-/// Get the high 31 bits of a 48-bit integer (for `lrand48()` and `nrand48()`).
-pub fn x_to_uint31(x: u64) -> c_long {
-    (x >> 17) as c_long
-}
-
-/// Get the high 32 bits, signed, of a 48-bit integer (for `mrand48()` and
-/// `jrand48()`).
-pub fn x_to_int32(x: u64) -> c_long {
-    // Cast via i32 to ensure we get the sign correct
-    (x >> 16) as i32 as c_long
+/// Used by `srand48()` and `seed48()`.
+pub unsafe fn reset_a_and_c() {
+    A = A_DEFAULT_VALUE;
+    C = C_DEFAULT_VALUE;
 }
 
 /// Build a 48-bit integer from a size-3 array of unsigned short.
@@ -68,8 +45,42 @@ pub unsafe fn set_ushort_arr3_from_uint48(arr_ptr: *mut c_ushort, value: u64) {
     *arr_ptr.offset(2) = c_ushort::from((value >> 32) as u16);
 }
 
-/// Used by `srand48()` and `seed48()`.
-pub unsafe fn reset_a_and_c() {
-    A = A_DEFAULT;
-    C = C_DEFAULT;
+/// Advances the buffer from the input argument to the next element in
+/// the linear congruential generator's sequence.
+/// 
+/// Modifies the passed argument in-place and returns the new value as a
+/// u64. The input argument must be a size-3 array.
+pub unsafe fn generator_step(xi_arr_ptr: *mut c_ushort) -> u64 {
+    let old_xi: u64 = ushort_arr3_to_uint48(xi_arr_ptr);
+    
+    /* The recurrence relation of the linear congruential generator,
+     * X_(n+1) = (a * X_n + c) % m,
+     * with m = 2**48. The multiplication and addition can overflow a
+     * u64, but we just let it wrap since we take mod 2**48 anyway. */
+    let new_xi: u64 = A.wrapping_mul(old_xi).wrapping_add(u64::from(C)) & 0xffff_ffff_ffff;
+    
+    set_ushort_arr3_from_uint48(xi_arr_ptr, new_xi);
+    new_xi
+}
+
+/// Get a C `double` from a 48-bit integer (for `drand48()` and
+/// `erand48()`).
+pub fn x_to_float64(x: u64) -> c_double {
+    /* We set the exponent to 0, and the 48-bit integer is copied into the high
+     * 48 of the 52 significand bits. The value then lies in the range
+     * [1.0, 2.0), from which we simply subtract 1.0. */
+    f64::from_bits(0x3ff0_0000_0000_0000_u64 | (x << 4)) - 1.0f64
+}
+
+/// Get the high 31 bits of a 48-bit integer (for `lrand48()` and
+/// `nrand48()`).
+pub fn x_to_uint31(x: u64) -> c_long {
+    (x >> 17) as c_long
+}
+
+/// Get the high 32 bits, signed, of a 48-bit integer (for `mrand48()`
+/// and `jrand48()`).
+pub fn x_to_int32(x: u64) -> c_long {
+    // Cast via i32 to ensure we get the sign correct
+    c_long::from((x >> 16) as i32)
 }

src/header/stdlib/mod.rs

@@ -232,8 +232,8 @@ pub extern "C" fn div(numer: c_int, denom: c_int) -> div_t {
 
 #[no_mangle]
 pub unsafe extern "C" fn drand48() -> c_double {
-    lcg48::XI = lcg48::next_x(lcg48::XI);
-    lcg48::x_to_float64(lcg48::XI)
+    let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
+    lcg48::x_to_float64(new_xi)
 }
 
 // #[no_mangle]
@@ -248,9 +248,7 @@ pub extern "C" fn ecvt(
 
 #[no_mangle]
 pub unsafe extern "C" fn erand48(xsubi: *mut c_ushort) -> c_double {
-    let old_xi = lcg48::ushort_arr3_to_uint48(xsubi);
-    let new_xi = lcg48::next_x(old_xi);
-    lcg48::set_ushort_arr3_from_uint48(xsubi, new_xi);
+    let new_xi = lcg48::generator_step(xsubi);
     lcg48::x_to_float64(new_xi)
 }
 
@@ -366,9 +364,7 @@ pub extern "C" fn initstate(seec: c_uint, state: *mut c_char, size: size_t) -> *
 
 #[no_mangle]
 pub unsafe extern "C" fn jrand48(xsubi: *mut c_ushort) -> c_long {
-    let old_xi = lcg48::ushort_arr3_to_uint48(xsubi);
-    let new_xi = lcg48::next_x(old_xi);
-    lcg48::set_ushort_arr3_from_uint48(xsubi, new_xi);
+    let new_xi = lcg48::generator_step(xsubi);
     lcg48::x_to_int32(new_xi)
 }
 
@@ -385,7 +381,11 @@ pub extern "C" fn labs(i: c_long) -> c_long {
 #[no_mangle]
 pub unsafe extern "C" fn lcong48(param: *mut c_ushort) {
     // Input should be a size-7 array.
-    lcg48::XI = lcg48::ushort_arr3_to_uint48(param.offset(0));
+    
+    /* Go through this ptr -> u64 -> ptr conversion to ensure we only
+     * get the lower 16 bits of each element. */
+    let new_xi = lcg48::ushort_arr3_to_uint48(param.offset(0));
+    lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
     lcg48::A = lcg48::ushort_arr3_to_uint48(param.offset(3));
     lcg48::C = *param.offset(6) as u16; // c_ushort may be more than 16 bits
 }
@@ -425,8 +425,8 @@ pub extern "C" fn lldiv(numer: c_longlong, denom: c_longlong) -> lldiv_t {
 
 #[no_mangle]
 pub unsafe extern "C" fn lrand48() -> c_long {
-    lcg48::XI = lcg48::next_x(lcg48::XI);
-    lcg48::x_to_uint31(lcg48::XI)
+    let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
+    lcg48::x_to_uint31(new_xi)
 }
 
 #[no_mangle]
@@ -582,15 +582,13 @@ pub extern "C" fn mkstemps(name: *mut c_char, suffix_len: c_int) -> c_int {
 
 #[no_mangle]
 pub unsafe extern "C" fn mrand48() -> c_long {
-    lcg48::XI = lcg48::next_x(lcg48::XI);
-    lcg48::x_to_int32(lcg48::XI)
+    let new_xi = lcg48::generator_step(lcg48::DEFAULT_XI.as_mut_ptr());
+    lcg48::x_to_int32(new_xi)
 }
 
 #[no_mangle]
 pub unsafe extern "C" fn nrand48(xsubi: *mut c_ushort) -> c_long {
-    let old_xi = lcg48::ushort_arr3_to_uint48(xsubi);
-    let new_xi = lcg48::next_x(old_xi);
-    lcg48::set_ushort_arr3_from_uint48(xsubi, new_xi);
+    let new_xi = lcg48::generator_step(xsubi);
     lcg48::x_to_uint31(new_xi)
 }
 
@@ -710,12 +708,11 @@ pub unsafe extern "C" fn realpath(pathname: *const c_char, resolved: *mut c_char
 pub unsafe extern "C" fn seed48(seed16v: *mut c_ushort) -> *mut c_ushort {
     lcg48::reset_a_and_c();
     
-    //lcg48::STASHED_XI = lcg48::XI;
-    //lcg48::set_ushort_arr3_from_uint48(&mut lcg48::STASHED_XI[0] as *mut c_ushort, lcg48::XI);
-    lcg48::set_ushort_arr3_from_uint48(lcg48::STASHED_XI.as_mut_ptr(), lcg48::XI);
-    lcg48::XI = lcg48::ushort_arr3_to_uint48(seed16v);
+    lcg48::STASHED_XI = lcg48::DEFAULT_XI;
+    
+    let new_xi = lcg48::ushort_arr3_to_uint48(seed16v);
+    lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
     
-    //&mut lcg48::STASHED_XI[0]
     lcg48::STASHED_XI.as_mut_ptr()
 }
 
@@ -808,7 +805,8 @@ pub unsafe extern "C" fn srand48(seedval: c_long) {
     /* Set the high 32 bits of the 48-bit X_i value to the lower 32 bits
      * of the input argument, and the lower 16 bits to 0x330e, as
      * specified in POSIX. */
-    lcg48::XI = (((seedval as u32) as u64) << 16) | 0x330e_u64;
+    let new_xi = (((seedval as u32) as u64) << 16) | 0x330e_u64;
+    lcg48::set_ushort_arr3_from_uint48(lcg48::DEFAULT_XI.as_mut_ptr(), new_xi);
 }
 
 // #[no_mangle]