diff options
Diffstat (limited to 'sim/common/sim-alu.h')
| -rw-r--r-- | sim/common/sim-alu.h | 46 |
1 files changed, 23 insertions, 23 deletions
diff --git a/sim/common/sim-alu.h b/sim/common/sim-alu.h index 49d1018..925fdb8 100644 --- a/sim/common/sim-alu.h +++ b/sim/common/sim-alu.h @@ -36,7 +36,7 @@ Code using this module includes it into sim-main.h and then, as a convention, defines macro's ALU*_END that records the result of any - aritmetic performed. Ex: + arithmetic performed. Ex: #include "sim-alu.h" #define ALU32_END(RES) \ @@ -73,7 +73,7 @@ ALU*_RESULT: Generic ALU result output. ALU*_HAD_OVERFLOW: Returns a nonzero value if signed overflow - occured. + occurred. ALU*_OVERFLOW_RESULT: If the macro ALU*_HAD_OVERFLOW is being used this is the most efficient result available. Ex: @@ -84,8 +84,8 @@ (RES) = ALU16_OVERFLOW_RESULT ALU*_HAD_CARRY_BORROW: Returns a nonzero value if unsigned - overflow or underflow (also refered to as carry and borrow) - occured. + overflow or underflow (also referred to as carry and borrow) + occurred. ALU*_CARRY_BORROW_RESULT: If the macro ALU*_HAD_CARRY_BORROW is being used this is the most efficient result available. Ex: @@ -132,7 +132,7 @@ -/* Twos complement aritmetic - addition/subtraction - carry/borrow +/* Twos complement arithmetic - addition/subtraction - carry/borrow (or you thought you knew the answer to 0-0) @@ -154,9 +154,9 @@ UMAXn: The upper bound of an unsigned N bit value (the lower bound is always zero). - Un: UMAXn + 1. Unsigned arrithmetic is computed `modulo (Un)'. + Un: UMAXn + 1. Unsigned arithmetic is computed `modulo (Un)'. - X[p]: Is bit P of X. X[0] denotes the least signifant bit. + X[p]: Is bit P of X. X[0] denotes the least significant bit. ~X[p]: Is the inversion of bit X[p]. Also equal to 1-X[p], (1+X[p])mod(2). @@ -167,7 +167,7 @@ Overflow/Overflow indicates an error in computation of signed - arrithmetic. i.e. given X,Y in [MINn..MAXn]; overflow + arithmetic. i.e. given X,Y in [MINn..MAXn]; overflow indicates that the result X+Y > MAXn or X+Y < MIN_INTx. Hardware traditionally implements overflow by computing the XOR of @@ -179,7 +179,7 @@ Addition - Overflow - method 1: - Overflow occures when the sign (most significant bit) of the two N + Overflow occurs when the sign (most significant bit) of the two N bit operands is identical but different to the sign of the result: Rn = (Xn + Yn) @@ -191,7 +191,7 @@ The two N bit operands are sign extended to M>N bits and then - added. Overflow occures when SIGN_BIT<n> and SIGN_BIT<m> do not + added. Overflow occurs when SIGN_BIT<n> and SIGN_BIT<m> do not match. Rm = (SEXTn (Xn) + SEXTn (Yn)) @@ -203,7 +203,7 @@ The two N bit operands are sign extended to M>N bits and then - added. Overflow occures when the result is outside of the sign + added. Overflow occurs when the result is outside of the sign extended range [MINn .. MAXn]. @@ -235,7 +235,7 @@ Addition - Carry - Introduction: - Carry (poorly named) indicates that an overflow occured for + Carry (poorly named) indicates that an overflow occurred for unsigned N bit addition. i.e. given X, Y in [0..UMAXn] then carry indicates X+Y > UMAXn or X+Y >= Un. @@ -293,7 +293,7 @@ Given two signed N bit numbers, a carry can be detected by treating the numbers as N bit unsigned and adding them using M>N unsigned - arrithmetic. Carry is indicated by bit (1 << N) being set (result + arithmetic. Carry is indicated by bit (1 << N) being set (result >= 2**N). @@ -314,29 +314,29 @@ 0 <= X < Un, 0 <= Y < Un ==> X + Y < 2 Un - Consider Y when carry occures: + Consider Y when carry occurs: X + Y >= Un, Y < Un - ==> (Un - X) <= Y < Un # re-arange + ==> (Un - X) <= Y < Un # rearrange ==> Un <= X + Y < Un + X < 2 Un # add Xn ==> 0 <= (X + Y) mod Un < X mod Un - or when carry as occured: + or when carry as occurred: (X + Y) mod Un < X mod Un - Consider Y when carry does not occure: + Consider Y when carry does not occur: X + Y < Un have X < Un, Y >= 0 ==> X <= X + Y < Un ==> X mod Un <= (X + Y) mod Un - or when carry has not occured: + or when carry has not occurred: ! ( (X + Y) mod Un < X mod Un) - hence we get carry by computing in N bit unsigned arrithmetic. + hence we get carry by computing in N bit unsigned arithmetic. carry <- (Xn + Yn) < Xn @@ -360,7 +360,7 @@ ==> X + ~Y + 1 # -Y = ~Y + 1 In addition to the result, the equation produces Carry-out. For - succeeding extended prrcision calculations, the more general + succeeding extended precision calculations, the more general equation can be used: C[p]:R[p] = X[p] + ~Y[p] + C[p-1] @@ -416,7 +416,7 @@ Treating Xn and Yn as unsigned values then a borrow (unsigned - underflow) occures when: + underflow) occurs when: B = Xn < Yn ==> C = Xn >= Yn @@ -491,7 +491,7 @@ do { \ /* 32 bit target expressions: - Since most hosts do not support 64 (> 32) bit arrithmetic, carry + Since most hosts do not support 64 (> 32) bit arithmetic, carry method 4 and overflow method 4 are used. */ #define ALU32_BEGIN(VAL) \ @@ -518,7 +518,7 @@ alu32_v = 0 /* 64 bit target expressions: Even though the host typically doesn't support native 64 bit - arrithmetic, it is still used. */ + arithmetic, it is still used. */ #define ALU64_BEGIN(VAL) \ unsigned64 alu64_r = (VAL); \ |