From cb697da1d5c36ac4e75e554cbc279674dd7075f4 Mon Sep 17 00:00:00 2001 From: Michael Forney Date: Wed, 29 Sep 2021 14:51:49 -0700 Subject: eval: Avoid implementation-defined unsigned to signed conversions Instead, use an additional int64_t member in the union. Since exact-width integer types have no padding bits or trap representations, and use two's-complement representation, we can portably access an int64_t union member stored as uint64_t and vice-versa. This allows us to reinterpret the value without invoking potentially implementation-defined behavior of casting an unsigned integer to a signed integer type which may not be able to represent its value. --- cc.h | 1 + eval.c | 74 +++++++++++++++++++++++++++++++++--------------------------------- 2 files changed, 38 insertions(+), 37 deletions(-) diff --git a/cc.h b/cc.h index 9597d6e..51b8f86 100644 --- a/cc.h +++ b/cc.h @@ -328,6 +328,7 @@ struct expr { } ident; union { uint64_t u; + int64_t i; double f; } constant; struct { diff --git a/eval.c b/eval.c index 2590687..958f517 100644 --- a/eval.c +++ b/eval.c @@ -17,13 +17,13 @@ cast(struct expr *expr) else if (expr->type->prop & PROPINT && expr->type->basic.issigned) size |= S; switch (size) { - case 1: expr->constant.u = (uint8_t)expr->constant.u; break; - case 1|S: expr->constant.u = (int8_t)expr->constant.u; break; + case 1: expr->constant.u = (uint8_t)expr->constant.u; break; + case 1|S: expr->constant.u = (expr->constant.u & UINT8_MAX ^ INT8_MIN) - INT8_MIN; break; case 2: expr->constant.u = (uint16_t)expr->constant.u; break; - case 2|S: expr->constant.u = (int16_t)expr->constant.u; break; + case 2|S: expr->constant.u = (expr->constant.u & UINT16_MAX ^ INT16_MIN) - INT16_MIN; break; case 4: expr->constant.u = (uint32_t)expr->constant.u; break; - case 4|S: expr->constant.u = (int32_t)expr->constant.u; break; - case 4|F: expr->constant.f = (float)expr->constant.f; break; + case 4|S: expr->constant.u = (expr->constant.u & UINT32_MAX ^ INT32_MIN) - INT32_MIN; break; + case 4|F: expr->constant.f = (float)expr->constant.f; break; } } @@ -37,47 +37,47 @@ binary(struct expr *expr, enum tokenkind op, struct expr *l, struct expr *r) op |= S; switch (op) { case TMUL: - case TMUL|S: expr->constant.u = l->constant.u * r->constant.u; break; - case TMUL|F: expr->constant.f = l->constant.f * r->constant.f; break; - case TDIV: expr->constant.u = l->constant.u / r->constant.u; break; - case TDIV|S: expr->constant.u = (int64_t)l->constant.u / (int64_t)r->constant.u; break; - case TDIV|F: expr->constant.f = l->constant.f / r->constant.f; break; - case TMOD: expr->constant.u = l->constant.u % r->constant.u; break; - case TMOD|S: expr->constant.u = (int64_t)l->constant.u % (int64_t)r->constant.u; break; + case TMUL|S: expr->constant.u = l->constant.u * r->constant.u; break; + case TMUL|F: expr->constant.f = l->constant.f * r->constant.f; break; + case TDIV: expr->constant.u = l->constant.u / r->constant.u; break; + case TDIV|S: expr->constant.i = l->constant.i / r->constant.i; break; + case TDIV|F: expr->constant.f = l->constant.f / r->constant.f; break; + case TMOD: expr->constant.u = l->constant.u % r->constant.u; break; + case TMOD|S: expr->constant.i = l->constant.i % r->constant.i; break; case TADD: - case TADD|S: expr->constant.u = l->constant.u + r->constant.u; break; - case TADD|F: expr->constant.f = l->constant.f + r->constant.f; break; + case TADD|S: expr->constant.u = l->constant.u + r->constant.u; break; + case TADD|F: expr->constant.f = l->constant.f + r->constant.f; break; case TSUB: - case TSUB|S: expr->constant.u = l->constant.u - r->constant.u; break; - case TSUB|F: expr->constant.f = l->constant.f - r->constant.f; break; + case TSUB|S: expr->constant.u = l->constant.u - r->constant.u; break; + case TSUB|F: expr->constant.f = l->constant.f - r->constant.f; break; case TSHL: - case TSHL|S: expr->constant.u = l->constant.u << r->constant.u; break; - case TSHR: expr->constant.u = l->constant.u >> r->constant.u; break; - case TSHR|S: expr->constant.u = (int64_t)l->constant.u >> r->constant.u; break; + case TSHL|S: expr->constant.u = l->constant.u << (r->constant.u & 63); break; + case TSHR: expr->constant.u = l->constant.u >> (r->constant.u & 63); break; + case TSHR|S: expr->constant.i = l->constant.i >> (r->constant.u & 63); break; case TBAND: - case TBAND|S: expr->constant.u = l->constant.u & r->constant.u; break; + case TBAND|S: expr->constant.u = l->constant.u & r->constant.u; break; case TBOR: - case TBOR|S: expr->constant.u = l->constant.u | r->constant.u; break; + case TBOR|S: expr->constant.u = l->constant.u | r->constant.u; break; case TXOR: - case TXOR|S: expr->constant.u = l->constant.u ^ r->constant.u; break; - case TLESS: expr->constant.u = l->constant.u < r->constant.u; break; - case TLESS|S: expr->constant.u = (int64_t)l->constant.u < (int64_t)r->constant.u; break; - case TLESS|F: expr->constant.u = l->constant.f < r->constant.f; break; - case TGREATER: expr->constant.u = l->constant.u > r->constant.u; break; - case TGREATER|S: expr->constant.u = (int64_t)l->constant.u > (int64_t)r->constant.u; break; + case TXOR|S: expr->constant.u = l->constant.u ^ r->constant.u; break; + case TLESS: expr->constant.u = l->constant.u < r->constant.u; break; + case TLESS|S: expr->constant.u = l->constant.i < r->constant.i; break; + case TLESS|F: expr->constant.u = l->constant.f < r->constant.f; break; + case TGREATER: expr->constant.u = l->constant.u > r->constant.u; break; + case TGREATER|S: expr->constant.u = l->constant.i > r->constant.i; break; case TGREATER|F: expr->constant.u = l->constant.f > r->constant.f; break; - case TLEQ: expr->constant.u = l->constant.u <= r->constant.u; break; - case TLEQ|S: expr->constant.u = (int64_t)l->constant.u <= (int64_t)r->constant.u; break; - case TLEQ|F: expr->constant.u = l->constant.f <= r->constant.f; break; - case TGEQ: expr->constant.u = l->constant.u >= r->constant.u; break; - case TGEQ|S: expr->constant.u = (int64_t)l->constant.u >= (int64_t)r->constant.u; break; - case TGEQ|F: expr->constant.u = l->constant.f >= r->constant.f; break; + case TLEQ: expr->constant.u = l->constant.u <= r->constant.u; break; + case TLEQ|S: expr->constant.u = l->constant.i <= r->constant.i; break; + case TLEQ|F: expr->constant.u = l->constant.f <= r->constant.f; break; + case TGEQ: expr->constant.u = l->constant.u >= r->constant.u; break; + case TGEQ|S: expr->constant.u = l->constant.i >= r->constant.i; break; + case TGEQ|F: expr->constant.u = l->constant.f >= r->constant.f; break; case TEQL: - case TEQL|S: expr->constant.u = l->constant.u == r->constant.u; break; - case TEQL|F: expr->constant.u = l->constant.f == r->constant.f; break; + case TEQL|S: expr->constant.u = l->constant.u == r->constant.u; break; + case TEQL|F: expr->constant.u = l->constant.f == r->constant.f; break; case TNEQ: - case TNEQ|S: expr->constant.u = l->constant.u != r->constant.u; break; - case TNEQ|F: expr->constant.u = l->constant.f != r->constant.f; break; + case TNEQ|S: expr->constant.u = l->constant.u != r->constant.u; break; + case TNEQ|F: expr->constant.u = l->constant.f != r->constant.f; break; default: fatal("internal error; unknown binary expression"); } -- cgit v1.2.3