Bixnum masked create method

include/pablo/bixnum/bixnum.h

@@ -26,6 +26,8 @@ class BixNumCompiler {
 public:
     BixNumCompiler(PabloBuilder & pb) : mPB(pb) {}
     BixNum Create(unsigned val);
+    // Create a bixnum of the given value at mask positions, 0 elsewhere.
+    BixNum Create(PabloAST * mask, unsigned val);
     PabloAST * EQ(BixNum value, unsigned test, const llvm::StringRef &Name = "");
     PabloAST * EQ(BixNum value, BixNum test, const llvm::StringRef &Name = "");
     PabloAST * NEQ(BixNum value, unsigned test, const llvm::StringRef &Name = "");

lib/pablo/bixnum/bixnum.cpp

@@ -186,7 +186,8 @@ BixNum BixNumCompiler::HighBits(BixNum value, unsigned highBitCount) {
 }
 
 BixNum BixNumCompiler::Create(unsigned value) {
-    unsigned value_bits = floor_log2(value)+1;
+    unsigned value_bits = 1;
+    if (value > 0) value_bits = floor_log2(value)+1;
     BixNum v(value_bits);
     for (unsigned i = 0; i < value_bits; i++) {
         if ((value & (1<<i)) == 0) {
@@ -198,6 +199,20 @@ BixNum BixNumCompiler::Create(unsigned value) {
     return v;
 }
 
+BixNum BixNumCompiler::Create(PabloAST * mask, unsigned value) {
+    unsigned value_bits = 1;
+    if (value > 0) value_bits = floor_log2(value)+1;
+    BixNum v(value_bits);
+    for (unsigned i = 0; i < value_bits; i++) {
+        if ((value & (1<<i)) == 0) {
+            v[i] = mPB.createZeroes();
+        } else {
+            v[i] = mask;
+        }
+    }
+    return v;
+}
+
 BixNum BixNumCompiler::AddModular(BixNum augend, unsigned addend) {
     addend = addend & ((1 << augend.size()) - 1);
     if (addend == 0) return augend;