Scaffolding for defining settings.

Settings can be defined globally or per-ISA. They are available to code through
a generated Settings struct with accessor methods per setting.

meta/gen_settings.py

@@ -0,0 +1,104 @@
+"""
+Generate sources with settings.
+"""
+
+import srcgen
+from cretonne import BoolSetting, NumSetting, settings
+
+
+def layout_group(sgrp):
+    """
+    Layout the settings in sgrp, assigning byte and bit offsets.
+
+    Return the next unused byte offset.
+    """
+    # Byte offset where booleans are allocated.
+    bool_byte = -1
+    # Next available bit number in bool_byte.
+    bool_bit = 10
+    # Next available whole byte.
+    next_byte = 0
+
+    for setting in sgrp.settings:
+        if isinstance(setting, BoolSetting):
+            # Allocate a bit from bool_byte.
+            if bool_bit > 7:
+                bool_byte = next_byte
+                next_byte += 1
+                bool_bit = 0
+            setting.byte_offset = bool_byte
+            setting.bit_offset = bool_bit
+            bool_bit += 1
+        else:
+            # This is a numerical or enumerated setting. Allocate a single
+            # byte.
+            setting.byte_offset = next_byte
+            next_byte += 1
+
+    return next_byte
+
+
+def gen_getter(setting, fmt):
+    """
+    Emit a getter function for `setting`.
+    """
+    fmt.doc_comment(setting.__doc__ + '.')
+
+    if isinstance(setting, BoolSetting):
+        proto = 'pub fn {}(&self) -> bool'.format(setting.name)
+        with fmt.indented(proto + ' {', '}'):
+            fmt.line('(self.bytes[{}] & (1 << {})) != 0'.format(
+                setting.byte_offset,
+                setting.bit_offset))
+    elif isinstance(setting, NumSetting):
+        proto = 'pub fn {}(&self) -> u8'.format(setting.name)
+        with fmt.indented(proto + ' {', '}'):
+            fmt.line('self.bytes[{}]'.format(setting.byte_offset))
+    else:
+        raise AssertionError("Unknown setting kind")
+
+
+def gen_getters(sgrp, fmt):
+    """
+    Emit getter functions for all the settings in fmt.
+    """
+    fmt.doc_comment("User-defined settings.")
+    with fmt.indented('impl Settings {', '}'):
+        for setting in sgrp.settings:
+            gen_getter(setting, fmt)
+
+
+def gen_default(sgrp, byte_size, fmt):
+    """
+    Emit a Default impl for Settings.
+    """
+    v = [0] * byte_size
+    for setting in sgrp.settings:
+        v[setting.byte_offset] |= setting.default_byte()
+
+    with fmt.indented('impl Default for Settings {', '}'):
+        fmt.doc_comment('Return a `Settings` object with default values.')
+        with fmt.indented('fn default() -> Settings {', '}'):
+            with fmt.indented('Settings {', '}'):
+                vs = ', '.join('{:#04x}'.format(x) for x in v)
+                fmt.line('bytes: [ {} ],'.format(vs))
+
+
+def gen_group(sgrp, fmt):
+    """
+    Generate a Settings struct representing `sgrp`.
+    """
+    byte_size = layout_group(sgrp)
+
+    fmt.doc_comment('Settings group `{}`.'.format(sgrp.name))
+    with fmt.indented('pub struct Settings {', '}'):
+        fmt.line('bytes: [u8; {}],'.format(byte_size))
+
+    gen_getters(sgrp, fmt)
+    gen_default(sgrp, byte_size, fmt)
+
+
+def generate(isas, out_dir):
+    fmt = srcgen.Formatter()
+    gen_group(settings.group, fmt)
+    fmt.update_file('settings.rs', out_dir)