hare

commit 0aa7dfdc9d77fab0ba0735a82730e2b5eb9c1d43
parent 181b5c0bd8827845c35801304f6431c80ed51a81
Author: Armin Preiml <apreiml@strohwolke.at>
Date:   Tue, 29 Nov 2022 13:24:00 +0100

crypto::bigint: add decrodd and isodd

Signed-off-by: Armin Preiml <apreiml@strohwolke.at>

Diffstat:
M
crypto/bigint/arithm.ha
 | 
6
++++++
M
crypto/bigint/util.ha
 | 
4
+++-

2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/crypto/bigint/arithm.ha b/crypto/bigint/arithm.ha
@@ -55,6 +55,12 @@ export fn sub(a: []word, b: const []word, do: u32) u32 = {
 	return carry;
 };
 
+// Decrements 1 from an odd integer 'x'.
+export fn decrodd(x: []word) void = {
+	assert(isodd(x));
+	x[1] ^= 1;
+};
+
 // Right-shift an integer 'x' by 'count'. The shift amount must be less than
 // [[WORD_BITSIZE]].
 export fn rshift(x: []word, count: word) void = {
diff --git a/crypto/bigint/util.ha b/crypto/bigint/util.ha
@@ -64,4 +64,6 @@ fn iszero(x: []word) u32 = {
 	free(y);
 };
 
-
+fn isodd(x: []word) bool = {
+	return x[1] & 1 == 1;
+};