Add vars to split the two Karatsuba sub-workspaces

1 files changed, 20 insertions, 14 deletions

diff --git a/src/lib/math/mp/mp_karat.cpp b/src/lib/math/mp/mp_karat.cpp
index 2ac03ac1e..220bd8f9e 100644
--- a/src/lib/math/mp/mp_karat.cpp
+++ b/src/lib/math/mp/mp_karat.cpp
@@ -101,6 +101,9 @@ void karatsuba_mul(word z[], const word x[], const word y[], size_t N,
    word* z0 = z;
    word* z1 = z + N;
 
+   word* ws0 = workspace;
+   word* ws1 = workspace + N;
+
    clear_mem(workspace, 2*N);
 
    /*
@@ -116,25 +119,25 @@ void karatsuba_mul(word z[], const word x[], const word y[], size_t N,
    const int32_t cmp0 = bigint_sub_abs(z0, x0, x1, N2);
    const int32_t cmp1 = bigint_sub_abs(z1, y1, y0, N2);
 
-   karatsuba_mul(workspace, z0, z1, N2, workspace+N);
+   karatsuba_mul(ws0, z0, z1, N2, ws1);
    const bool is_negative = cmp0 != cmp1;
 
    // Compute X_lo * Y_lo
-   karatsuba_mul(z0, x0, y0, N2, workspace+N);
+   karatsuba_mul(z0, x0, y0, N2, ws1);
 
    // Compute X_hi * Y_hi
-   karatsuba_mul(z1, x1, y1, N2, workspace+N);
+   karatsuba_mul(z1, x1, y1, N2, ws1);
 
-   const word ws_carry = bigint_add3_nc(workspace + N, z0, N, z1, N);
-   word z_carry = bigint_add2_nc(z + N2, N, workspace + N, N);
+   const word ws_carry = bigint_add3_nc(ws1, z0, N, z1, N);
+   word z_carry = bigint_add2_nc(z + N2, N, ws1, N);
 
    z_carry += bigint_add2_nc(z + N + N2, N2, &ws_carry, 1);
    bigint_add2_nc(z + N + N2, N2, &z_carry, 1);
 
    if(is_negative)
-      bigint_sub2(z + N2, 2*N-N2, workspace, N);
+      bigint_sub2(z + N2, 2*N-N2, ws0, N);
    else
-      bigint_add2_nc(z + N2, 2*N-N2, workspace, N);
+      bigint_add2_nc(z + N2, 2*N-N2, ws0, N);
    }
 
 /*
@@ -161,27 +164,30 @@ void karatsuba_sqr(word z[], const word x[], size_t N, word workspace[])
    word* z0 = z;
    word* z1 = z + N;
 
+   word* ws0 = workspace;
+   word* ws1 = workspace + N;
+
    clear_mem(workspace, 2*N);
 
    // See comment in karatsuba_mul
    bigint_sub_abs(z0, x0, x1, N2);
-   karatsuba_sqr(workspace, z0, N2, workspace+N);
+   karatsuba_sqr(ws0, z0, N2, ws1);
 
-   karatsuba_sqr(z0, x0, N2, workspace+N);
-   karatsuba_sqr(z1, x1, N2, workspace+N);
+   karatsuba_sqr(z0, x0, N2, ws1);
+   karatsuba_sqr(z1, x1, N2, ws1);
 
-   const word ws_carry = bigint_add3_nc(workspace + N, z0, N, z1, N);
-   word z_carry = bigint_add2_nc(z + N2, N, workspace + N, N);
+   const word ws_carry = bigint_add3_nc(ws1, z0, N, z1, N);
+   word z_carry = bigint_add2_nc(z + N2, N, ws1, N);
 
    z_carry += bigint_add2_nc(z + N + N2, N2, &ws_carry, 1);
    bigint_add2_nc(z + N + N2, N2, &z_carry, 1);
 
    /*
    * This is only actually required if cmp (result of bigint_sub_abs) is != 0,
-   * however if cmp==0 then workspace[0:N] == 0 and avoiding the jump hides a
+   * however if cmp==0 then ws0[0:N] == 0 and avoiding the jump hides a
    * timing channel.
    */
-   bigint_sub2(z + N2, 2*N-N2, workspace, N);
+   bigint_sub2(z + N2, 2*N-N2, ws0, N);
    }
 
 /*