1 files changed, 22 insertions, 0 deletions

diff --git a/src/lib/libcrypto/bn/old/info b/src/lib/libcrypto/bn/old/info
new file mode 100644
index 0000000000..5ac99c3b23
--- /dev/null
+++ b/src/lib/libcrypto/bn/old/info
@@ -0,0 +1,22 @@
+Given A1A0 * B1B0 == S3S2S1S0
+
+S0=     low(A0*B0)
+S1=     low( (A1-A0)*(B0-B1)) +low( A1*B1) +high(A0*B0)
+S2=     high((A1-A0)*(B0-B1)) +high(A1*B1) +low( A1*B1)
+S3=     high(A1*B1);
+
+Assume we know S1 and S0, and can calulate A1*B1 and high((A1-A0)*(B0-B1))
+
+k0=     S0 == low(A0*B0)
+k1=     S1
+k2=     low( A1*B1)
+k3=     high(A1*B1)
+k4=     high((A1-A0)*(B0-B1))
+
+k1=     low((A1-A0)*(B0-B1)) +k2 +high(A0*B0)
+S2=     k4 +k3 +k2
+S3=     k3
+
+S1-k2= low((A1-A0)*(B0-B1)) +high(A0*B0)
+
+We potentially have a carry or a borrow from S1