From: Kaz Wesley Date: Sun, 18 Mar 2018 06:07:24 +0000 (-0700) Subject: MIM design: elaborate on RVECTOR access X-Git-Url: https://jxself.org/git/?p=muddle.git;a=commitdiff_plain;h=979815bcd1845744f665ad405c7de449edbfffa7 MIM design: elaborate on RVECTOR access Signed-off-by: Kaz Wesley --- diff --git a/doc/mim.md b/doc/mim.md index b2af24d..20de59e 100644 --- a/doc/mim.md +++ b/doc/mim.md @@ -130,14 +130,18 @@ which enables simplifications like a fallthrough implementation for ops that have one variant that takes an immediate in the B position and another variant (with a different opcode) that takes a local. -Operand types can be: -- immediate Byte (incl. signed offset for must jump operations) -- immediate Word (offset for the "long jumps"--JUMP/EMP?/FALSE?) -- index into the current function's Constants table -- index into the current function's Locals table -- index into the Locals table containing an LVAR to be dereferenced -Generally each opcode has a fixed interpretation of each operand; any -necessary variants are encoded as separate opcodes rather than +The address modes are: +- B: immediate Byte (incl. signed offset for most jump operations) +- H: immediate Halfword (16-bit operand, incl long jumps JUMP/EMP?/FALSE?) +- W: IP-relative Word (32 bit constant inlined in code) +- L: index into the current function's Locals table +- LL: index into the Locals table, result indirected through a locative +The RVECTOR is placed at local0, so that static values can be accessed +via NTHR and locals with static names via NTHRL. + +An opcode interprets each of its arguments according to a fixed +address mode; any necessary variants are encoded as separate opcodes +(distinguished in assembly by the suffixes listed above) rather than branching on flag bits. The only common non-guard branches are the opcode dispatch, (occasionally prefixed-opcode dispatch), and dispatch for polymorphic/mistyped ops.