Add post-quantum wallet support and PQ transaction signing

app/src/main/cpp/pq/mldsa65/rounding.c

@@ -0,0 +1,102 @@
+#include <stdint.h>
+#include "params.h"
+#include "rounding.h"
+
+/*************************************************
+* Name:        power2round
+*
+* Description: For finite field element a, compute a0, a1 such that
+*              a mod^+ Q = a1*2^D + a0 with -2^{D-1} < a0 <= 2^{D-1}.
+*              Assumes a to be standard representative.
+*
+* Arguments:   - int32_t a: input element
+*              - int32_t *a0: pointer to output element a0
+*
+* Returns a1.
+**************************************************/
+int32_t power2round(int32_t *a0, int32_t a)  {
+  int32_t a1;
+
+  a1 = (a + (1 << (D-1)) - 1) >> D;
+  *a0 = a - (a1 << D);
+  return a1;
+}
+
+/*************************************************
+* Name:        decompose
+*
+* Description: For finite field element a, compute high and low bits a0, a1 such
+*              that a mod^+ Q = a1*ALPHA + a0 with -ALPHA/2 < a0 <= ALPHA/2 except
+*              if a1 = (Q-1)/ALPHA where we set a1 = 0 and
+*              -ALPHA/2 <= a0 = a mod^+ Q - Q < 0. Assumes a to be standard
+*              representative.
+*
+* Arguments:   - int32_t a: input element
+*              - int32_t *a0: pointer to output element a0
+*
+* Returns a1.
+**************************************************/
+int32_t decompose(int32_t *a0, int32_t a) {
+  int32_t a1;
+
+  a1  = (a + 127) >> 7;
+#if GAMMA2 == (Q-1)/32
+  a1  = (a1*1025 + (1 << 21)) >> 22;
+  a1 &= 15;
+#elif GAMMA2 == (Q-1)/88
+  a1  = (a1*11275 + (1 << 23)) >> 24;
+  a1 ^= ((43 - a1) >> 31) & a1;
+#endif
+
+  *a0  = a - a1*2*GAMMA2;
+  *a0 -= (((Q-1)/2 - *a0) >> 31) & Q;
+  return a1;
+}
+
+/*************************************************
+* Name:        make_hint
+*
+* Description: Compute hint bit indicating whether the low bits of the
+*              input element overflow into the high bits.
+*
+* Arguments:   - int32_t a0: low bits of input element
+*              - int32_t a1: high bits of input element
+*
+* Returns 1 if overflow.
+**************************************************/
+unsigned int make_hint(int32_t a0, int32_t a1) {
+  if(a0 > GAMMA2 || a0 < -GAMMA2 || (a0 == -GAMMA2 && a1 != 0))
+    return 1;
+
+  return 0;
+}
+
+/*************************************************
+* Name:        use_hint
+*
+* Description: Correct high bits according to hint.
+*
+* Arguments:   - int32_t a: input element
+*              - unsigned int hint: hint bit
+*
+* Returns corrected high bits.
+**************************************************/
+int32_t use_hint(int32_t a, unsigned int hint) {
+  int32_t a0, a1;
+
+  a1 = decompose(&a0, a);
+  if(hint == 0)
+    return a1;
+
+#if GAMMA2 == (Q-1)/32
+  if(a0 > 0)
+    return (a1 + 1) & 15;
+  else
+    return (a1 - 1) & 15;
+#elif GAMMA2 == (Q-1)/88
+  if(a0 > 0)
+    return (a1 == 43) ?  0 : a1 + 1;
+  else
+    return (a1 ==  0) ? 43 : a1 - 1;
+#endif
+}