From b4701bb4d5b9c0c6240cce5ff7aac5bd2be274f7 Mon Sep 17 00:00:00 2001 From: Igor M Date: Mon, 11 Mar 2024 13:20:08 +0200 Subject: [PATCH] Comment the push int function --- src/hbas.c | 36 ++++++++++++++++++++++++++++++++---- 1 file changed, 32 insertions(+), 4 deletions(-) diff --git a/src/hbas.c b/src/hbas.c index eb3b3e9..df3c15c 100644 --- a/src/hbas.c +++ b/src/hbas.c @@ -110,16 +110,44 @@ size_t label_lookup(LabelVec *labels, char *name, size_t len) { return INVALID; } -// safety: assumes the buffer has enough place for specified integer size +// safety: assumes the buffer has enough place for specified integer size. +// `sign` is a bitset, where bit `1` indicates that value accepts a signed int, +// and bit `2` indicates that value accepts an unsigned int. AsmError push_int_le(char *buf, uint64_t val, size_t size, uint8_t sign) { - int valid_uint = val >> (size * 8) == 0; + // Unsigned integers must have all upper bits set to zero. To check this, + // we shift the value right by the integer size and verify it equals zero. + int valid_uint = (val >> (size * 8)) == 0; + + // For signed integers, the sign-extended high bits must match the sign bit. + // By shifting right by one less than the total bit size (size * 8 - 1), + // we isolate the sign bit and any sign-extended bits. For a value fitting + // in the signed range, this operation results in either 0 (for non-negative + // values) or -1 (for negative values due to sign extension). int64_t int_shifted = ((int64_t)val) >> (size * 8 - 1); - int valid_int = int_shifted == 0 || (~int_shifted) == 0; - // Note: this assumes the format for `sign` is a bitset. + + // To unify the check for both positive and negative cases, we adjust + // non-zero values (-1) by incrementing by 1. This turns -1 into 0, + // enabling a single check for 0 to validate both cases. This adjustment + // simplifies the validation logic, allowing us to use a single condition to + // check for proper sign extension or zero extension in the original value. + int_shifted += int_shifted != 0; + + // A valid signed integer will have `int_shifted` equal to 0 + // after adjustment, indicating proper sign extension. + int valid_int = int_shifted == 0; + + // Validity bitmask to represents whether the value + // fits as signed, unsigned, or both. int validity = valid_int | (valid_uint << 1); + + // If the value's validity doesn't match the `sign` requirements, + // we report an overflow. if ((validity & sign) == 0) { return ErrImmediateOverflow; } + + // Write out the bytes of the integer to the buffer in little-endian order, + // starting with the lowest byte first. for (size_t ii = 0; ii < size; ii += 1) { buf[ii] = val & 0xff; val >>= 8;