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Implement $countbits function

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Michael Singer 2021-02-23 00:55:55 +01:00 committed by Zachary Snow
parent 22bed38540
commit 8434ba5a3b
1 changed files with 59 additions and 0 deletions
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59
frontends/ast/simplify.cc
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@ -3089,6 +3089,65 @@ skip_dynamic_range_lvalue_expansion:;
goto apply_newNode; goto apply_newNode;
} }
if (str == "\\$countbits") {
if (children.size() < 2)
log_file_error(filename, location.first_line, "System function %s got %d arguments, expected at least 2.\n",
RTLIL::unescape_id(str).c_str(), int(children.size()));
std::vector<RTLIL::State> control_bits;
// Determine which bits to count
for (size_t i = 1; i < children.size(); i++) {
AstNode *node = children[i];
while (node->simplify(true, false, false, stage, -1, false, false)) { }
if (node->type != AST_CONSTANT)
log_file_error(filename, location.first_line, "Failed to evaluate system function `%s' with non-constant control bit argument.\n", str.c_str());
if (node->bits.size() != 1)
log_file_error(filename, location.first_line, "Failed to evaluate system function `%s' with control bit width != 1.\n", str.c_str());
control_bits.push_back(node->bits[0]);
}
// Detect width of exp (first argument of $countbits)
int exp_width = -1;
bool exp_sign = false;
AstNode *exp = children[0];
exp->detectSignWidth(exp_width, exp_sign, NULL);
newNode = mkconst_int(0, false);
for (int i = 0; i < exp_width; i++) {
// Generate nodes for: exp << i >> ($size(exp) - 1)
// ^^ ^^
AstNode *lsh_node = new AstNode(AST_SHIFT_LEFT, exp->clone(), mkconst_int(i, false));
AstNode *rsh_node = new AstNode(AST_SHIFT_RIGHT, lsh_node, mkconst_int(exp_width - 1, false));
AstNode *or_node = nullptr;
for (RTLIL::State control_bit : control_bits) {
// Generate node for: (exp << i >> ($size(exp) - 1)) === control_bit
// ^^^
AstNode *eq_node = new AstNode(AST_EQX, rsh_node->clone(), mkconst_bits({control_bit}, false));
// Or the result for each checked bit value
if (or_node)
or_node = new AstNode(AST_LOGIC_OR, or_node, eq_node);
else
or_node = eq_node;
}
// We should have at least one element in control_bits,
// because we checked for the number of arguments above
log_assert(or_node != nullptr);
delete rsh_node;
// Generate node for adding with result of previous bit
newNode = new AstNode(AST_ADD, newNode, or_node);
}
goto apply_newNode;
}
if (current_scope.count(str) != 0 && current_scope[str]->type == AST_DPI_FUNCTION) if (current_scope.count(str) != 0 && current_scope[str]->type == AST_DPI_FUNCTION)
{ {
AstNode *dpi_decl = current_scope[str]; AstNode *dpi_decl = current_scope[str];